FAIRFIELD, Iowa — Bernie Sanders touted his consistency on progressive issues Thursday, subtly contrasting himself with fellow Democratic presidential candidate Hillary Clinton as he stumped in this progressive bastion.

“It’s easy to swim with the tide,” Sanders said to a crowd of 900 as he ticked off a laundry list of issues on which he’s held liberal stances over the years. “But when the going gets rough, some of us were there, and some of us were not there.”

“I don’t have to apologize, because I voted against DOMA,” he remarked about the Defense of Marriage Act, which was signed into law by Clinton’s husband, former president Bill Clinton.

Sanders has been stepping up his contrasts with the former secretary of state in the final days before the Iowa caucuses — now just four days away.

RELATED: Doctor: Bernie Sanders in ‘overall very good health’

Earlier in the day Thursday, his campaign released one if its toughest ads yet. The ad highlights Goldman Sachs’ role in the financial collapse of 2008 and says the company exerts undue influence in the political process through campaign contributions and speaking fees to politicians and former politicians.

While the ad does not mention Clinton by name or implication, Sanders has made reference to the donations and speaking fees she’s taken from the Wall Street bank and the ad is clearly aimed at existing supporters who are familiar with that information.

Fairfield is known as a liberal enclave in an otherwise rural part of the state, and was a stronghold for Barack Obama in his 2008 race against Clinton. Sanders strategists are hoping to repeat the Obama playbook, including running up the score with a large number of delegates in places like this, while Clinton is thought to be stronger in more rural areas.

“We’re not too worried about whether we can win. We want to give Bernie a mandate,” Sam Farling, the county-wide organizer for Sanders here, told MSNBC.

To do that, organizers need to convert the excitement shown at events like this into actual turnout at caucuses. “For the sake of our kids, for the sake of our country, we cannot fail,” Sanders said. “Let’s win on Monday.”

In the morning, Sanders visited a high school in Des Moines where he made a pitch for young people to get involved in the political process.

“A lot of times young people don’t think politics is hip. They don’t think it’s cool,” he said. “Football: yes. Partying: yes. Politicos: no. That’s kind of dumb.”

He went on to say that students should fight cynicism about politics. “If people your age say you’re dumb, why do you care about these things? I hope you look them in the eye and say, I am concerned about the future of this country, and say you’re the dumb guy, not me,” he said.