The Vermont senator, at a CNN town hall, underscored his background makes him the better candidate for the Democratic presidential nomination. He attacked former Secretary of State Clinton on her vote on the Iraq war, something he was against.
"Experience is important, but it is not the only thing," Sanders said.
Sanders, Clinton and former Maryland Gov. Martin O'Malley made their arguments to Iowa voters at a televised forum hosted by Drake University and the Iowa Democratic Party, one week ahead of the Iowa caucuses. The forum came as polls show a narrowing between Clinton and Sanders in early voting states that also include New Hampshire.
Sanders attempted to show Clinton as a flip-flopper on issues including the Trans-Pacific Partnership and the Keystone pipeline.
"On Day 1, I said the Keystone Pipeline is a dumb idea," Sanders said, "Why did it take Hillary Clinton such a long time before she came into opposition to the Keystone Pipeline?"
Clinton fought back, stressing the central theme in her campaign: Her wide-ranging experience makes her the best candidate. Answering a question from a Sanders supporter about young voters' sense she is dishonest, she detailed a history of Republican-led attacks against her.
"They throw all this stuff at me, and I'm still standing," Clinton said, adding that the attacks come "because I've been on the front lines of change and progress since I was your age."
Clinton also said she was "really touch and gratified" after receiving a boost from President Barack Obama in Politico.
"She can govern and she can start here, Day 1, more experienced than any non-vice president has ever been who aspires to this office," he said in the interview published earlier Monday.
O'Malley, who also served as mayor of Baltimore, defended his record on racial issues and policing, again defending his "all lives matter" response to "black lives matter" protesters.
In Iowa's caucuses, a candidate must get 15 percent of voter support to gain delegates. Asked what he would tell his supporters if he fails to meet the 15 percent, O'Malley declined to speculate.
"My message to the O'Malley supporters is this: 'Hold strong at your caucus,'" he said.