U.S. Sen Bernie Sanders pledged Saturday to support the eventual Democratic nominee for president and avoid efforts to belittle others in the crowded contest.

"Donald Trump must be defeated," he said, carefully emphasizing each word, to a rousing crowd at the Iowa State Fairgrounds in Des Moines.

Sanders brought his "political revolution" back to Iowa this week with three rallies across the state. In gearing up his stump at his last stop, the senator made a point to underscore his support for defeating the current president.

He said he knew many candidates vying for the nomination and noted many serve alongside him in the U.S. Senate.

"Many of them are friends," he said. "Without exception, they are good people.”

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Sanders, an independent from Vermont, has been criticized by some mainstream Democrats who question his allegiance to the party. In her campaign memoir, former Secretary of State Hillary Clinton blamed Sanders for opening the door for Donald Trump's "Crooked Hillary" rhetoric.

While Sanders vigorously opposed Clinton in the 2016 primary, he endorsed her bid to defeat Trump and campaigned for her in the general election.

On Saturday, he said he hopes to run a campaign that is not based on "belittling people" or opposition research, but about substantive issues.

"I'm going to work as hard as I can, and I think we stand a very good chance of winning this nomination," he said. "But if we do not win, I will strongly support the Democratic nominee and hope and believe that others feel exactly the same way."

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