ALBUQUERQUE — Neil Mondragon watched with approval at an auto repair shop recently as Representative Heather A. Wilson, a New Mexico Republican visiting her district, dropped into the pit and drained the oil from a car.
Afterward, Mr. Mondragon recalled how he had backed Ms. Wilson, a supporter of the Iraq war, in her race for Congress two years ago. He, too, supported the war.
But now, Mr. Mondragon said, it is time to bring the troops home. And he is leaning toward voting for Ms. Wilson's opponent, Patricia Madrid, who has called for pulling the troops out of Iraq by the end of the year.
"The way I see the situation is, we have done what we had to," said Mr. Mondragon, 27, whose brother fought in the war and returned with post-traumatic stress disorder. "I don't see the point of having so many guys over there right now. We can't just stay there and baby-sit forever."
Mr. Mondragon is far from alone in reassessing his view of the war that has come to define George W. Bush's presidency.
Mr. Bush is pressing ahead with an intensified effort to shore up support for the war, but an increasingly skeptical and pessimistic public is putting pressure on Congress about the wisdom behind it, testing the political support for the White House's determination to remain in Iraq.
The results have been on display over the past week as members of Congress returned home and heard first-hand what public opinion polls have been indicating.
"We have been there now for three years, and we have suffered more losses than I think most people thought we would see," Representative Steve Chabot, an Ohio Republican from a relatively conservative district near Cincinnati, said in an interview on Friday. "You may have the president or others now who say we always knew this would be a long slog, but I think most people did not expect it to be as hard as it has been."
In Connecticut, Representative Christopher Shays, a Republican who is one of the Democrats' top targets this year in the midterm elections, has distanced himself from the White House even as he has emphasized his support for the war, saying the administration has made "huge mistakes" by allowing looting, disbanding the Iraqi army and failing to have enough troops on the ground
Senator Mike DeWine, an Ohio Republican who is also facing a tough re-election challenge, said that "people are not optimistic about what they see."
Even Representative Ileana Ros-Lehtinen, a Florida Republican who has made her support for the war a centerpiece of her campaign, said the public seemed "to be losing patience" with the war.
Interviews with voters, elected officials and candidates around the country suggest a deepening and hardening opposition to the war. Historians and analysts said this might mark a turning point in public perception.
"I'm less optimistic because I see the fatalities every day," said Angela Kirby, 32, a lawyer from St. Louis who initially supported the war. "And the longer it goes on, the less optimistic I am."
Here in New Mexico, Dollie Shoun, 67, said she had gone from being an ardent supporter of the war and the president to a fierce critic of both.
"There has been too many deaths, and it is time for them to come back home," Ms. Shoun said. Speaking of Mr. Bush, she added: "I was very much for him, but I don't trust him at this point in time."
Polls have found that support for the war and expectations about its outcome have reached their lowest level since the invasion. A Pew Research Center poll this week found that 66 percent of respondents said the United States was losing ground in preventing a civil war in Iraq, a jump of 18 percent since January.
The Pew poll also found that 49 percent now believed that the United States would succeed in Iraq, compared with 60 percent last July. A CBS News poll completed two weeks ago found that a majority (54 percent) believed Iraq would never become a stable democracy.
Richard B. Wirthlin, who was the pollster for President Ronald Reagan, says he sees the beginning of a decisive turn in public opinion against the war. "It is hard for me to imagine any set of circumstances that would lead to an enhancement of the public support that we have seen," he said. "It is more likely to go down, and the question is how far and how fast."
Even more problematic for the administration, pollsters have found, is that Americans who have soured on the war include many independent voters and some self-described Republicans.
William Kristol, editor of the conservative Weekly Standard, argued that views on the war remained fluid and that the White House could still rally support for the effort if Americans "are convinced we can win."
A perception of progress on the ground could help turn public opinion back toward Mr. Bush's way, some analysts said. As it is, a significant number of Americans, including a majority of Republicans, want Mr. Bush to continue the war.
"Bush is right in being optimistic," said Susan Knapp, 64, a Florida Republican. "I listened to the news this morning and there are people who think he's out of touch with reality, but in fact I think he knows better than most of us about what is going on, and he does know the situation."
And in interviews, some respondents said they agreed with Mr. Bush and Vice President Dick Cheney that journalists were exaggerating the bad news. "I have quite a few friends who have served over there and they come back with a different story than the media portrays," said Jerry Brown, a Republican in Fairfield County, Conn.
For Mr. Bush today, as it was for Presidents Lyndon B. Johnson and Richard M. Nixon decades ago, the question is how long can he continue fighting an unpopular war without it crippling his presidency by eroding trust in his judgment and credibility.
"Once the public loses confidence in a president's leadership at a time of war, once they don't trust him anymore, once his credibility is sharply diminished, how does he get it back?" said Robert Dallek, a historian who has written biographies of Johnson and Nixon.
The anxiety about the war could be seen in contested districts around the country. In recent weeks, Representative Wilson of New Mexico has been sharply critical of the administration on issues like domestic surveillance and its public projections about the war. Ms. Wilson said she worried that public opinion could turn decisively against the war in Iraq as it did during the Vietnam War. "Wasn't it Kissinger who said the acid test of foreign policy is public support?" she said.
In Connecticut, Diane Farrell, a Democrat challenging Mr. Shays, said she had consistently run into voters who drew comparisons between Iraq and Vietnam.
"People are throwing up their hands between the civil unrest, the number of deaths and the cost to taxpayers," Ms. Farrell said. "People feel worn out by the war, and they don't see an end. "
At the Capitol recently, Senator John W. Warner, a Virginia Republican who was the secretary of the Navy during part of the Vietnam War, was introduced to a visiting Iraqi. Mr. Warner proceeded to lecture her about the need for Iraqis to form a new government, and fast.
"The American people have a mind of their own," he told her, recalling how he watched during the Vietnam War as public opinion turned against the conflict — and inevitably Congress followed. In a later conversation, Mr. Warner said that such a moment had not been reached yet, but he warned that he sensed a "certain degree of impatience" in the country and around the world.
Copyright 2006 The New York Times Company