US Senator Michael Bennet, a Democrat from Colorado, announced yesterday he is running for president, just weeks after undergoing surgery for prostate cancer. His entry in the race brings to 21 the number of Democrats seeking to challenge Donald Trump in 2020, making for a sprawling fight for the party’s nomination.

“We cannot be the first generation to leave less to our kids, not more. That’s why I’m running for President,” Bennet said on Twitter.

“Let’s build opportunity for every American and restore integrity to our government,” he said. Bennet, 54, had said in March he was contemplating a run, but those plans were put on hold after he revealed he had been diagnosed with prostate cancer.

He underwent surgery in mid-April, and a spokesperson told Politico at the time that his doctors had said it was “completely successful and he requires no further treatment.”