"It's embarrassing for the Senate. It's embarrassing for our party," said Sen. John Ensign of Nevada, who leads the GOP's Senate campaign committee.

"I think it's best for the U.S. Senate, it's best for certainly his party, that he just keeps his word," Ensign told reporters outside the Senate chamber Thursday. "He gave us his word he would do something, and he's backing out on us, and I don't think that's the right thing to do."

A judge ruled Thursday that Craig's guilty plea to a misdemeanor disorderly conduct charge could not be withdrawn. Craig entered the plea after his June arrest in a men's room at the Minneapolis-St. Paul International Airport for allegedly propositioning a plainclothes police officer for sex.

After news of his arrest and guilty plea broke in August, the senator announced that he would resign at the end of September, but he postponed that move while seeking to have his guilty plea withdrawn.

However, after the judge's ruling Thursday, Craig said he'll remain in the Senate and study "additional legal options" -- much to the consternation of some GOP colleagues. Watch how Craig's decision poses a challenge for GOP leaders »

Sen. John Thune, R-South Dakota, called the issue "a distraction" for the party.

"I would have hoped he would have done what he said he was going to do," added Sen. Norm Coleman, R-Minnesota.

"He's chosen not to. The people of Idaho will have to speak to that, and the Ethics Committee will have to speak to that," Coleman said, referring to the Senate panel's indication that it will investigate Craig's conduct.

Fellow Idahoan Sen. Mike Crapo was a rare voice in the caucus, issuing a statement in support of Craig's decision.

"I look forward to serving with him as we continue to work on issues important to Idaho," Crapo said.

But in Boise, a spokesman for Idaho Gov. C.L. "Butch" Otter said that the Republican governor already has settled on a replacement for Craig -- but won't name the choice until the senator steps down.

Spokesman Jon Hanian denied that Otter, a longtime friend, is pushing Craig to go, saying the governor "just wants to be ready."

A Craig resignation would give an appointee the advantage of being in office for a year or more before the next election. Craig said he won't seek re-election in 2008, a decision advisers said he had made earlier.

The lack of an Idaho incumbent -- if that happens -- would complicate things for the GOP in what already is shaping up to be a difficult 2008 election.

Four other Republican senators -- John Warner of Virginia, Chuck Hagel of Nebraska, Wayne Allard of Colorado and Pete Domenici of New Mexico -- have announced they will not seek re-election, and at least four others are expected to face tough races.

"Democrats are cheering today," the Idaho Statesman newspaper said in an editorial urging Craig to go ahead and resign.

"He and we will be distracted by a Senate Ethics Committee and its hearings, which could be public, in what is certain to be brutally ugly, possibly on live TV, and centered on men having sex with men," the editorial warned.

Jasper LiCalzi, a political science professor at Albertson College of Idaho, told the Idaho Statesman that some voters still back Craig.

"There is core support here that thinks Craig has been railroaded, and there's another group that thinks he should stick it out," LiCalzi told the newspaper.

In his statement Thursday, Craig said any replacement would lack the seniority and committee assignments "that are valuable to Idaho." In addition, he said he wanted to clear his name before the Senate Ethics Committee.

One of Craig's attorneys, Stanley Brand, said on NBC's "Today" show Friday that Craig is considering appealing the judge's ruling and seems willing to risk a Ethics Committee inquiry.

"What he is saying is in 220 years of recorded history ... the Senate has never disciplined anyone for misdemeanor conduct that has nothing to do with official duties," Brand said on "Today." "So, while the Senate theoretically could do that, it hasn't, and our position is there is no reason to start now after 220 years."

"It's kind of like horse racing. If you're a horse that does well in the last sprint, you wait. But if you wait too long, there's going to be too much distance for you to catch up and you're not going to make it," said Steffen Schmidt, professor of political science at Iowa State University.

While supporters are impressed with Obama's signs of strength - his fund-raising prowess, the huge crowds at rallies, the Internet following - some are getting anxious that he hasn't risen in the polls.

"I am worried that he hasn't done more to close the gap," said a New York lawyer who has donated the maximum $2,300 to Obama's campaign and spoke on condition of anonymity. "It's positive that he hasn't fallen farther behind."

Preeta Bansal, a New York supporter, said she's not concerned.

"It's going to be a long fall. The race is just beginning and he's on fire," said Bansal, referring to recent stump speeches where she said he's been "superb."

New York City Councilman James Sanders, a Queens Democrat who supports Obama, conceded that supporters are "always concerned" and looking for the candidate to shine. But he said there's tremendous excitement for Obama, and real optimism that he can knock out Clinton.

"On the ground, the people, the groundswell is growing," Sanders said.

To overtake Clinton, the Obama campaign plans to drive home the message that the battle comes down to the following question: "Who do people think is most likely to bring about the change we need?"

David Axelrod, a top Obama adviser, said the Illinois senator won't hesitate to draw sharp contrasts with Clinton where contrasts are "germane and real." But don't expect a smackdown any time soon.

"I know there's a rooting interest, a kind of blood lust in the political community to see a kind of steel-cage match between Obama and Hillary," Axelrod said. "I don't think that's either politically smart or consistent with who he is."

The campaign has pinned much of its strategy on winning Iowa. Polls show Obama is in a close three-way race there with Clinton and John Edwards.

The campaign also has begun to deploy staff and build up ground operations in the states holding primaries on Feb. 5. And in the coming months, star supporter Oprah Winfrey "will do some things for us," Axelrod said.

"To me that's a continuation of the war," Edwards said. "Combat missions mean that the war is continuing. I believe the war needs to be brought to an end."

Edwards' broadside put Clinton on the defensive at a time when she is enjoying a comfortable lead in opinion polls and trying to appear above the fray. But there was no sign that the debate would prompt a major shake-up in the Democratic field.

"There may be a continuing counter-terrorism mission," she said, while adding that "the vast majority" of American troops would be out of Iraq by the end of her prospective first term in 2013.

The cross-fire on the campus of Dartmouth College came at the first debate of the critical autumn season leading up to the early voting contests in January ahead of the November 2008 election to replace President George W. Bush.

Iraq was a dominant theme of the debate as Democrats seek a way to force Bush to change his war strategy, which may leave as many as 100,000 troops there by the time the next president is inaugurated in January 2009.

He urged the U.N. to reform its Human Rights Council, which in the past has been chaired by Libya and other dictatorships, and said that the United States was open to an overhaul of the U.N. Security Council. The council is made up of the United States, Russia, China, Britain and France. Bush said he thought Japan was "well qualified" for membership.

The president began a three-day visit to New York on Monday for the 62rd meeting of the General Assembly. He met privately at the Waldorf-Astoria Hotel with Mahmoud Abbas, president of the Palestinian Authority, and Tony Blair, the former British prime minister who now represents the quartet -- the United States, Russia, the United Nations and the European Union -- seeking to bring about a broad peace agreement between the Palestinians and Israel.

The General Assembly speech today veered away from the themes of terrorism and war that were the foundation of Bush's first speeches at the U.N. Instead, he turned to elements of foreign policy that carry less of an edge while still encouraging the spread of democracy and the fight against tyranny.

The shift in tone comes at a time when Bush is struggling in a political world grown increasingly unfriendly, both at home and abroad.

It was at the U.N. last year that Venezuelan President Hugo Chavez -- never a friend of Bush -- likened the American president to a visitor from the underworld, saying, "The devil came here yesterday, and it smells of sulfur still today."

But even international allies are growing skittish. Britain, under new Prime Minister Gordon Brown, hopes to scale down its commitment of troops in Iraq. And at home, notwithstanding the Democrats' inability to force Bush's hand in Iraq, there are few signs that public opposition to the war is weakening.

The president's history of laying out a hard line and challenging the United Nations to join him frequently has left him searching for friends in an organization that has been described with scorn by the White House.

By contrast, the call for cooperation on a humanitarian agenda "certainly is a stronger message for a U.S. president than challenging the relevance of the United Nations," said P.J. Crowley, a senior fellow and the director for homeland security at the liberal Center for American Progress in Washington.

Johanns was expected to announce his candidacy as early as Monday for the seat being vacated by fellow Republican Chuck Hagel after two terms. Analysts say Johanns would be the front-runner of four men seeking the GOP nomination.

Nebraska is a Republican-leaning state. Democrats have talked of recruiting Bob Kerrey, a former U.S. senator and Nebraska governor who is now a university president in New York City. Democrats control the Senate, 51-49.

As agriculture secretary, the mild-spoken Johanns pressed U.S. trading partners to remove barriers to U.S. beef, erected out of fears of mad cow disease, and to expand farm exports, which account for a quarter of farm income. He took the lead in administration proposals to deny farm subsidies to the wealthiest Americans.

In his resignation letter to Bush, Johanns said the U.S. farm sector "is stronger than ever before," with high crop prices and record farm exports.

"After careful thought and difficult deliberation, I am writing to inform you that I have decided to pursue a new opportunity to serve this great nation," wrote Johanns.

Nebraska is a major grain and cattle-producing state. Democrats in Nebraska said Johanns was leaving USDA without completing an important task -- overhaul of U.S. farm policy this year.

Johanns resigned as governor to become agriculture secretary in January 2005. Born in Iowa, Johanns practiced law in western Nebraska before election as mayor of Lincoln, the state capital, in 1991 en route to the governorship in 1998. He once said that for a former farm boy, being agriculture secretary was a dream job.

Deputy Agriculture Secretary Charles Conner was named acting secretary until Bush nominates a permanent replacement.

The Agriculture Department, with 100,000 employees, is in charge of crop subsidies, the national forests, a vast research network and public nutrition programs including school lunch and food stamps.

Ferd Hoefner of the Sustainable Agriculture Coalition, said Johanns was the first USDA chief in decades to try to rein in farm payments and to show interest in beginning farmers.

But lawmakers have faulted Johanns for the faltering campaign to create a nationwide animal-tracking system, originally embraced by the administration as a key safeguard against mad cow and other fearsome diseases. USDA relies on voluntary participation in the program.

"He has been a clear and open advocate for ethanol within the administration," said Jay Truitt of the National Cattlemen's Beef Association. Truitt said Johanns "was the first to understand" how the explosive growth of the fuel ethanol industry would squeeze livestock and meat producers.

White House spokeswoman Dana Perino said the president hoped the US Senate, controlled by Bush's Democratic foes, would confirm Mukasey to replace the scandal-stained Alberto Gonzales before going into recess on October 8.

Gonzales, a close Bush confidant, left the post under a cloud, with Democratic and Republican critics alike charging that he lacked independence from the White House, was incompetent, hid the truth and may be guilty of perjury.

A former top aide to Gonzales revealed earlier this year that she improperly used political criteria in hiring decisions, and Democrats have been probing whether a mass purge of federal prosecutors was tied to political, not legal, considerations.

The nomination could have far-reaching implications for several pitched battles over Bush administration anti-terrorism policies, like warrantless spying on US citizens.

Democratic Majority Leader Harry Reid said Mukasey had "strong professional credentials a reputation for independence" and suggested the former judge "knows how to say no to the president when he oversteps the Constitution."

"But there should be no rush to judgment. The Senate Judiciary Committee must carefully examine Judge Mukasey's views on the complex legal challenges facing the nation," Reid said in a statement.

Democratic Senator Patrick Leahy, chairman of the Judiciary Committee that will take up the nomination before it goes to a vote, promised to review Mukasey's qualifications "a serious and deliberate fashion."

But in a potential hurdle to Mukasey, Leahy also warned that he would take into account White House "cooperation" on existing requests for information on issues like the mass firings and the warrantless surveillance program.

"The next attorney general needs to be someone who can begin the process of restoring the Department of Justice to its proper mission," Leahy, one of Gonzales's fiercest critics, said in a statement.

At the Rose Garden ceremony, which Gonzales did not attend, Mukasey thanked the embattled official for his "support and encouragement" but did not praise his record or his management of the Justice Department.

Mukasey said the department faced "vastly different" challenges from when he served there 35 years ago "but the principles that guide the department remain the same: To pursue justice by enforcing the law with unswerving fidelity to the Constitution."

Mukasey, 66, was appointed a federal district judge in New York under Republican former president Ronald Reagan and retired in 2006, returning to private practice.

He presided over several high-profile terrorism legal cases, including the trial of Omar Abdel-Rahman, the so-called "blind sheikh" who was convicted as the master of a 1993 attack on New York's World Trade Center towers.

Mukasey generally has been supportive of Bush administration policies in the war on terror, although he has at times ruled against the president.

He served as a district judge in the case of Jose Padilla, the US citizen accused by the Bush administration of being an enemy combatant who conspired to kill Americans overseas.

Mukasey upheld the Bush administration's right to detain Padilla indefinitely without charges -- a decision later reversed -- but ruled that he was entitled to a lawyer -- a position the administration argued against.

"That decision hardly makes Mukasey a wild-eyed civil libertarian," said Mark Agrast, a senior fellow with the left-of-center Center for American Progress think tank in Washington.

"But his insistence that the government give Padilla access to counsel was a rare act of principle at a time when few in Congress or the courts were willing to defy the administration," said Agrast.