Four decades before David Petraeus's appearance on Capitol Hill on Monday, another respected general reported to Washington on another unpopular war, using arguments strikingly similar to what's being heard today.

"We will be able to phase down the level of our military effort, withdraw some troops with the understanding that the Vietnamese will be prepared to take over functions that are now being performed by our troops," Gen. William Westmoreland declared confidently.

Westmoreland, a man then considered credible by all sides in the war debate, was relating a genuine improvement in U.S. fortunes during a bloody year in Vietnam.

Watch FOXNews.com for live coverage Monday of the Petraeus-Crocker hearing at 12:30 ET.

Weeks later, the enemy launched the Tet Offensive, taking staggering losses but proving its staying power. U.S. combat deaths in Vietnam would more than double before America finally got out.

Gen. Petraeus, the Iraq war commander, enters the hearing room Monday with the admiration of Republicans, the wary respect of Democrats who have otherwise savaged President Bush's war policy, and a lot riding on his words.

He will report on progress in Iraq, paired — as Westmoreland was in his Washington optimism offensive — by the U.S. ambassador from the war zone.

And he'll stand in the shadow of a parade of generals called to account for wars won and lost.

Congress has a rich and checkered tradition of dealing with generals. Some of the most inept civilian advice on the conduct of warfare ever came from a committee that thought it knew better than Abraham Lincoln's commanders how to run the Civil War.

History has judged that, at times, the civilians did know better.

Another committee cut Gen. Douglas MacArthur down to size in 1951, deftly exposing the flaws that had led President Harry Truman to remove him as Korean war commander for insubordination. A hero to millions when Truman sacked him, MacArthur left the hearing room closer to plainly human.

Chalk one up for lawmakers, who are inevitably second-guessers in a time of war.

"There's a lot of people who are armchair generals who reside here in the air-conditioned comfort of Capitol Hill," observed Arizona Sen. John McCain, a Republican presidential hopeful and stout defender of the 2007 troop increase.

In the Civil War, the hawkish Joint Committee on the Conduct of the War pressed outdated tactics and demands for quicker, tougher action on military officers schooled in doctrine and seasoned in the battlefield. There was no air conditioning, but plenty of hot air, in the view of historian Bruce Tap, author of "Over Lincoln's Shoulder."

"They were ideologically moral men who advocated just and ethical causes, but they were also narrow-minded partisans, blinded by their own sense of importance and self-righteousness," he wrote in the Journal of the Abraham Lincoln Association in 2002.

"Most of the time, they consumed time and resources with little practical influence on the Northern war effort."

Generals are more likely to be venerated on Capitol Hill than roasted, even when wars are going badly. It's the commander in chief who takes the heat.

"There's not much political pay dirt in attacking generals," said John Mueller, a professor of political science at Ohio State and an authority on war, the presidency and public opinion. "Anyway, it doesn't do any good. Except maybe for MacArthur, they do try to stay out of politics and they're generally pretty good at that."

But testifying has not always been a great career move.

Major Gen. George Armstrong Custer embarrassed his superiors when, in congressional testimony, he verified allegations that federal agents had taken money for Indian reservations. By some historical accounts, the resulting shortages on the reservations sent Indians back out to fight.

Custer's 1876 testimony cost him his command. He got it back in time to engage those Indians at Little Big Horn and die there with his men — no whistle-blower protections for him.

Less dramatic but unmistakable consequences befell Gen. Eric Shinseki, the Army chief of staff who upset his civilian bosses in 2003 when he testified that it might take several hundred thousand U.S. troops to control Iraq after the coming invasion.

His words were prophetic but he was out of the job within months. He left with the warning, "Beware a 12-division strategy for a 10-division army."

In 1967, President Lyndon Johnson attributed much of the anti-war sentiment to partisan objections to him and felt there was a positive story to be told about Vietnam.

Westmoreland stepped forward with his "light-at-the-end-of-the-tunnel talks" to members of Congress and the press, Mueller said. "Objectively, you could say that things were better."

But as it turned out, he added, "the tunnel was very long."

Watch FOXNews.com for live coverage Monday of the Petraeus-Crocker hearing.