Hillary Clinton’s career as a senator was relatively short. The former First Lady served just one and a half terms in the upper chamber, spending most of 2007 and 2008 campaigning for president, and resigning in 2009 to serve as Barack Obama’s secretary of state. But one critical Senate vote—a “yea” cast in favor of invading Iraq, arguably the most important vote of her career—continues to haunt Clinton in her second White House bid, as Monday night’s Democratic town hall showed.

Much like Obama in 2008, Bernie Sanders, an upstart candidate who has surprised the political establishment by challenging Clinton in the polls, used his time in the spotlight during the CNN-hosted event to remind voters that the former secretary of state, despite her claim to have a superior grasp of foreign policy, voted in 2002 to send troops to Iraq. Sanders was not blunt about his views: “I think that war is a dumb idea,” he said, calling the decision to launch the deeply unpopular war “the most significant vote and issue regarding foreign policy that we have seen in this country in modern history.”

“I voted against the war in Iraq, and if you go to my Web site, listen to the speech that I gave when I was in the House in 2002, saying, yes, it's easy to get rid of a dictator like Saddam Hussein, but there’s going to be a political vacuum, there will be instability,” he continued, alluding to the rise of extremist groups in the wake of Hussein’s fall.

For many Democrats now supporting Sanders, Clinton’s years of foreign-policy experience are easily negated by her judgment on that one issue, a point the Vermont senator hammered repeatedly Monday night, even comparing Clinton’s experience to that of former vice president and Iraq war architect Dick Cheney. “Secretary Clinton was secretary of state of this country for four years. That is a lot of experience . . . but judgement is also important. And, my own point was in talking Dick Cheney, he had a lot of experience, too. His policies with regard to foreign affairs was an absolute disaster.”

As the clock ticks down to the Iowa caucuses on February 1, pundits have been unable to refrain from drawing more parallels between the Clinton of 2016 and 2008. While the Iraq war was fresh in the minds of Democrats back in 2008 (when 81 percent of them opposed the war), any hopes that Iraq would be less of an issue eight years later were dashed by the rise of ISIS, a roiling war in Syria, and growing tensions between Iran and Saudi Arabia. Clinton’s foreign policy experience has always been a double-edged sword, spanning everything from her misadventures in Bosnia to the attack on Benghazi. Now, with the the establishment front-runner once again in danger of losing Iowa, Sanders is trying his hardest to remind Democratic voters why they had their doubts in the first place.