DES MOINES, Iowa ― Former Vice President Joe Biden has played a role in some of the most controversial domestic and foreign policy decisions from the 1970s to the 2010s.

He co-authored the 1994 crime bill, lobbied for the 2005 bankruptcy reform bill, and voted for both the North American Free Trade Agreement and the Iraq War. Despite that record, Biden began the presidential race as a front-runner and continues to top the polls in early states, including several recent surveys in Iowa, the first-in-the-nation caucus state where he had previously been weaker.

Foreign policy and international trade, previously lightly discussed, took up large chunks of time. And while there were disagreements between the candidates Tuesday night, in the final stretch before the Iowa caucuses, they largely avoided aggressively attacking one another. Warren and Sanders passed on re-litigating what happened in their 2018 meeting, and Biden avoided a pile-on about the Iraq War and his support for international trade deals protested bitterly by labor unions.

The decision to avoid head-on fights was motivated no doubt by the fact that much of the Democratic electorate seems to have little appetite for such squabbles, preferring the focus be kept on attacking Trump and not doing too much lasting damage for the general election.

The greatest beneficiary of the debate’s calm tone was Biden. Tuesday night’s debate was the last chance Iowans had to hear Biden answer in greater detail about his record before they head to caucus sites on Feb. 3.

ROBYN BECK/Getty Images The debate moderators and most candidates declined to press former Vice President Joe Biden about the many controversial elements of his four-decade policy record.

But at the CNN/Des Moines Register Democratic presidential debate on Tuesday night, Biden’s legislative record got less scrutiny from the moderators and his fellow candidates than, say, the potential costs of “Medicare for All” and Sanders’ assorted other social policies.

Sanders, who has for weeks been hammering Biden for supporting the Iraq War and approving trade deals that cost the country manufacturing jobs, did his best to initiate discussions with Biden on both fronts.

Sanders noted that he and Biden were both in Congress in 2002 during the vote to authorize the Iraq War, but unlike Biden, he did not believe Bush administration officials’ claims about the threat Iraq posed.

“I thought they were lying. I didn’t believe them for a moment. I took to the floor,” he said. “I did everything I could to prevent that war. Joe saw it differently.”

In response, Biden declined to engage Sanders directly, focusing instead on his support for withdrawing combat troops during the Obama administration.

“I was asked to bring 156,000 troops home from that war, which I did,” Biden said. “I led that effort.”

The moderators, from CNN and the Des Moines Register, could have pressed Biden to answer directly for Sanders’ criticism, or explain whether withdrawing those troops ended up being a mistake given the rise of the so-called Islamic State, but they did not follow up with him ― and neither did any of the other candidates on the stage.

Sanders also blasted Biden for voting to authorize NAFTA and permanent normalized trade relations with China, which he said cost the country 4 million jobs.

“Joe and I have a fundamental disagreement here ― in case you haven’t noticed,” Sanders said, eliciting laughter from the audience. “And that is, NAFTA, PNTR with China, other trade agreements ― were written for one reason alone, and that is to increase the profits of large multinational corporations.”

Biden reacted by agreeing with Sanders on the need for greater “corporate responsibility” and expounding on the need for tougher enforcement of existing laws as well.

He did not directly answer for his votes for those trade agreements or explain his thinking. And once again, neither the moderators nor the other candidates joined in to press Biden.

Several other controversial elements of Biden’s record did not make it into the debate at all, including his authorship of the 1994 crime bill blamed for the explosion of the carceral state, his role in advocating for a 2005 law making it harder for households to declare bankruptcy, and his past support for cutting Social Security benefits. Even Sanders, whose campaign intimated that the Vermont senator would use the debate to attack Biden for that last stance, declined to engage in that line of questioning.

Sanders, Warren and Klobuchar engaged in a spirited discussion of the potential milestone of the first female president, which was spurred by Warren’s allegation that Sanders had told her privately in 2018 that he thought a woman could not get elected. (Sanders denies saying that.)

But Biden’s comments about gender earlier this month did not come up during the debate.

At a campaign event in Iowa, Biden recalled how Hillary Clinton had suffered sexist attacks during her 2016 presidential run, but said, “That’s not going to happen with me.”

Biden’s campaign told HuffPost that he had not intended to cast doubt on a woman’s ability to win the White House, but he has yet to answer for it personally and the moderators did not ask him about it.