U.S. Sen. Michael Bennet of Colorado jumped into the packed Democratic presidential primary on Thursday, announcing a 2020 campaign that had been stalled while he was treated for prostate cancer.

Bennet, a former head of Denver Public Schools who has carved out a reputation as a policy-oriented moderate, made his announcement on CBS’ “CBS This Morning,” saying the country faces two “enormous challenges,” among others: “One is the lack of economic mobility and opportunity for most Americans, and the other is the need to restore integrity to our government.”

“I think we need to do both of those things,” he said.

The son of a former ambassador to India and a Yale law school graduate who worked in the Clinton administration, Bennet worked for Republican billionaire Phil Anschutz when he moved to Colorado in the late 1990s. But when he re-entered public life, he did so as a Democrat, serving as chief of staff to then-Denver Mayor John Hickenlooper. Hickenlooper went on to become Colorado governor and now is also competing for the Democratic presidential nomination .

The presence of two moderate Coloradans who started their political careers in Denver City Hall reflects how crowded the Democratic presidential field has become. Bennet’s understated style and distaste for the sound bites required in a political campaign have usually led to speculation that he’d seek a Cabinet position rather than try to become the next president. But he began moving to assemble a presidential bid late last year and planned an announcement in April. He had to pause after being diagnosed with prostate cancer this spring.

Bennet, 54, told Colorado journalist Mike Littwin that he’d resume the campaign if he was treated successfully but that he wanted to make a point by disclosing his medical condition.

“I don’t want to be hysterical, but if it was left in me undetected, it could kill me,” Bennet said. “It won’t because I have insurance and decent medical care. The idea that the richest country in the world hasn’t figured out how to have universal health care is beyond embarrassing. It’s devastating.”

Bennet has been a vocal opponent in the Democratic Party of the push for single-payer health care championed by Sen. Bernie Sanders of Vermont, another 2020 presidential candidate. Instead, Bennet proposes letting consumers buy into Medicare through insurance exchanges, arguing that that will be a more efficient and realistic path to universal coverage. Likewise, Bennet has pushed back against arguments by some other presidential hopefuls that Democrats should respond to Republican tactics by expanding the size of the Supreme Court, saying the party needs to avoid the same scorched-earth tactics that, he says, its main rival employs.

Indeed, in a 4-minute launch video released Thursday morning, Bennet positioned himself as a truth teller willing to level with voters.

“I’m not going to pretend free college is the answer,” he said. “I’m not gonna say there’s a simple solution to a problem if I don’t believe there is one.”

Despite his professorial reputation, Bennet has shown an ability to be a tough campaigner. Appointed in 2009, Bennet won his first election in 2010 by pounding his Republican rival for opposing abortion rights and comparing homosexuality to alcoholism, eking out a narrow win in an otherwise disastrous year for Bennet’s party. Four years later, Bennet chaired the Democratic Senatorial Campaign Committee, a position that put him in contact with a network of national donors who also can help fund a presidential campaign.

Bennet gained internet fame this year when he blasted Republican Sen. Ted Cruz of Texas for backing a bill to pay Coast Guard members during the partial government shutdown but not reopen the government. Bennet said Cruz once led a 16-day government shutdown in a failed bid to derail funding for the Affordable Care Act at a time when Colorado was experiencing catastrophic flooding, delaying relief efforts.

“When the senator from Texas shut this government down in 2013, my state was flooded,” Bennet shouted. “People were killed. People’s houses were destroyed. Their small businesses were destroyed, forever.”

Bennet accused Cruz of crying “crocodile tears” this time around.

Cruz responded on the Senate floor by saying Bennet “spent a great deal of time yelling” and “attacking me personally.”

“I think we should discuss issues and substance and facts and not simply scream and yell at each other,” Cruz said.