Vermont independent Sen. Bernie Sanders on Thursday declared “we’re in this race to win” and highlighted key areas he’ll seek to differentiate himself from Hillary Clinton in the Democratic presidential primary.

“If you try to put together a movement which says, ‘We have got to stand together as a people and say that this Capitol, this beautiful Capitol, our county belongs to all of us and not the billionaire class’ -- that is not raising an issue, that is winning elections,” he said.

Sanders, who announced in an interview late Wednesday that he will run for president as a Democrat, became the first official primary challenger to Clinton’s campaign. He plans to formally announce his campaign on May 26 in Burlington, Vermont, where he once served as mayor.

Sanders faces an uphill battle against Clinton’s well-funded operation, but the self-described socialist is hoping to pick up momentum from the left-wing of the Democratic party that feels Clinton is too moderate on some key issues.

ANALYSIS: Bernie Sanders Won't Win. But His Ideas Might

The two-term senator mentioned his fierce opposition to the war in Iraq, which Clinton voted for, as one area he'll contrast himself with the former secretary of state.

“Many of the things I said back then turned out to be true, the massive destabilization in the region” Sanders said.

Another main focus of Sanders' campaign will be on income inequality and the power that millionaires and billionaires have in modern-day politics. The country, he said, faces more crises than at any other time since the Great Depression.

But the outspoken and passionate progressive also made clear Thursday that he has no interest in going on the offensive against Clinton.

“I’ve never run a negative ad in my life...What elections are about is serious debate over serious issue. Not political gossip, not making campaigns in soap operas,” Sanders said. “This is not the Red Sox versus the Yankees.”

Clinton welcomed Sanders into the race with a tweet: