WASHINGTON — Sen. Bernie Sanders, I-Vt., has for years cast his opposition to the Iraq War as near-absolute, insisting he knew the Bush administration was "lying" from the start about the threat to the U.S. posed by Saddam Hussein and his regime's alleged production of weapons of mass destruction.

"I listened very carefully, and I concluded that they were lying through their teeth. And I not only voted against that war, but I helped lead the opposition," Sanders said in a debate Feb. 7 in New Hampshire.

"I didn't believe them for a moment. I took to the floor. I did everything I could to prevent that war," he said in a debate in January.

But a review of the congressional record and statements before the House vote in October 2002 to authorize the U.S. to use military force show that his position wasn't as absolute as he claims.

At a time when Congress was debating how much authority to give the administration of President George W. Bush, Sanders made it clear on the House floor that his concern was about unilateral action by the U.S., not the administration's claims of weapons of mass destruction, or WMDs, which he appeared to accept as at least a possibility.

There are significant differences between Sanders and some Democrats, like former Sens. Joe Biden and Hillary Clinton, on Iraq. Unlike those two, Sanders voted against the final bill to authorize Bush to use military force and warned that it would be a "blank check" for war.

Still, Sanders reached the same conclusion on one aspect that many Democrats did at the time, including Biden, after listening to the intelligence: that the threat from Iraq wasn't "imminent" and that the U.S. shouldn't act unilaterally.

He didn't publicly raise doubts about U.S. intelligence that Iraq possessed WMDs until 2003, and he voted in favor of military intervention under specific circumstances, which was defeated in favor of the broader authorization approved by Congress.

In fact, Sanders' vote for a failed amendment, considered an "alternative," put him in the company of 147 Democrats looking for a way to restrain — but not necessarily stop — Bush from going to war. Biden, with whom Sanders has drawn sharp contrasts on the campaign trail, sponsored a similar failed amendment in the Senate that would have required U.N. blessing for any military conflict.

Rep. Barbara Lee of California was among a small number of Democrats against military force under any circumstance, and she voted against the alternative measure. In an interview, Lee said she believed some of her colleagues who voted for the alternative "wanted it both ways."

"We had enough information to know there were no weapons there," she said.

"You'd have to ask other members why they voted for that," she added. "I think they wanted to keep the door open [to war] in case the inspectors found something."

When asked about Sanders, Lee, who hasn't endorsed a presidential candidate, declined to comment on anyone in specific.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

When Sanders says he knew Bush was "lying," he's referring to the imminence of the threat, the Sanders campaign told NBC News. Furthermore, a majority of the original anti-war caucus voted for the alternative while also voting against the ultimate Iraq War resolution.

The measure would have authorized U.S. troops to participate, "by force if required," in eliminating Iraq's weapons of mass destruction and long-range missiles. It also requested that Bush return to Congress for authorization if the United Nations failed to organize an international coalition.

The amendment's sponsor, former Rep. John Spratt, D-S.C., made it clear that the measure gave Bush the option to act without U.N. approval if necessary.

"There is no difference with respect to our assessment of Saddam Hussein," Spratt said during floor debate on Oct. 10, 2002. "Those of us who support this substitute see him as a menace and a threat."

If "the Iraqis defy the inspectors and the Security Council fails to take action, fails to respond, the U.S. will be faced with going it alone," he said.

The Sanders campaign said the amendment was designed to "stop the Bush administration's push for war," because Bush would have had to go back to Congress for authorization if the U.N. failed to act.

Yet news coverage at the time, including in The New York Times, made it clear that the measure was a messaging instrument for Democrats who wanted to indicate that they "supported military action under the right circumstances."

Download the NBC News app for breaking news and politics

Sanders made it clear on the House floor on Oct. 9, 2002, that his concerns about Iraq centered on acting alone and the aftermath of a hasty invasion: "If a unilateral American invasion of Iraq is not the best approach, what should we do?" he asked.

"These inspectors should undertake an unfettered search for Iraqi weapons of mass destruction and destroy them when found pursuant to past U.N. resolutions. If Iraq resists inspection and elimination of stockpiled weapons, we should stand ready to assist the U.N. in enforcing compliance," he said. "There is more danger of an attack on the United States if we launch a precipitous invasion."

And Sanders had previously voiced his support for a U.S. policy to oust Hussein. In the years leading up to the war, Sanders voted for a U.S. policy of regime change, for example in 1996 in response to Hussein's having sent troops into Kurdish territory, and in October 1998 he backed the Iraq Liberation Act, which made regime change official U.S. policy.

"Mr. Speaker, Saddam Hussein is a brutal dictator who should be overthrown, and his ability to make weapons of destruction must be eliminated," he said on the House floor in December 1998.

Still, Sanders was by all accounts an avid opponent of the 2002 vote granting Bush Iraq war powers. He was part of a House anti-war coalition that held news conferences. He did interviews on major news outlets expressing opposition to the use-of-force resolution.

His position contrasted brightly with that of some Democrats at the time, including Clinton, who represented New York in the Senate and was the Democratic Party's presidential nominee in 2016. She took the floor and asserted that Hussein was working to rebuild his biological, chemical and nuclear capabilities.

But Sanders and many Democrats focused their doubts on the imminence of the threat from Iraq. It wasn't until 2003 that Sanders, as part of a Vermont delegation effort, called for an investigation into whether the Bush administration had manipulated intelligence information.

"Repeatedly, he [Bush] told us we were in danger of an attack from Iraq's weapons of mass destruction," Sanders said in a joint statement from the delegation that June. "Now it appears that much of the intelligence reflected significant doubts about the correctness of the assertion."

Sanders has made his opposition to the Iraq War a central part of both his 2016 and 2020 presidential campaigns. He has been hitting Biden hard over his Iraq War vote, including in a recent ad. "I did everything I could to prevent that war. Joe saw it differently," Sanders said in a debate Jan. 14 in Iowa.

The biggest difference between Sanders and many Democrats was how they ultimately voted.

Biden, then chairman of the Foreign Relations Committee, is on the record as having pressed George Tenet, then the director of the CIA, during a classified hearing for evidence backing up intelligence claims that Hussein had acquired aluminum tubes used to enrich uranium before the war.

Like Sanders, he made his reservations about an immediate strike clear.

"We should be compelling Iraq to make good on its obligations to the United Nations," Biden said on the Senate floor. "Because while Iraq's illegal weapons of mass destruction do not — do not — pose an imminent threat to our national security, in my view, they will if left unfettered."

Unlike Sanders, Biden ultimately voted to give Bush the authorization he sought.

In the most recent debate, Biden reiterated that he "made a mistake" in voting for the authorization.

"I trusted George Bush to keep his word. He said he was not going to go into Iraq. He said he was only using this to unite the United Nations to insist we get inspectors in," Biden said.