Sen. Bernie Sanders accused Hillary Clinton of taking an increasingly aggressive stance against him because she’s nervous that he is beating her in the race for the Democratic presidential nomination.

“It could be that the inevitable candidate for the Democratic nomination may not be so inevitable today,” Sanders said at the Iowa Brown & Black Forum in Des Moines Monday night. The forum, which began in 1984, featured the three Democratic presidential candidates appearing separately to answer questions about issues that affect the country’s growing minority population.

The Vermont senator added that Clinton may have noticed that his supporters have more “enthusiasm” than hers.

Clinton’s lead among likely Iowa caucus-goers shrank to just three percentage points in the latest NBC News/Wall Street Journal poll, and Sanders maintains a narrow lead over Clinton in New Hampshire.

Clinton has attacked Sanders in recent days for his 2005 vote that protected gun manufacturers from lawsuits. “I was there, I voted against it. Sen. Obama was there, he voted against it. And Sanders voted for it,” Clinton told the Des Moines Register editorial board earlier Monday. Asked about it at the forum, Sanders refused to say that vote had been a mistake, standing behind it as a “complicated” piece of legislation that protected small business owners.

Gov. Martin O’Malley hit Clinton on immigration, pointing out that she had supported deporting the surge of Central American children who arrived on the border in recent years. Clinton said she thinks the unaccompanied children should all be provided with lawyers to help argue their cases in immigration court.

During her turn at the forum, Clinton barely mentioned Sanders, instead focusing on her positions on immigration reform, abortion rights and gun control. She also answered a question about whether and how she had benefited from “white privilege,” saying, “Where do I start?”

When asked specifically if she thought Sanders could win, Clinton joked, “Anybody can win. Who would have thought Donald Trump would be leading in national polls?” The audience laughed. “Those of you who ever thought about running for president, take heart.”