During his tenure, Mr. Bennet has developed a reputation as a studious senator with a habit of mulling decisions for weeks. He has bucked the more liberal base of his party on a number of big issues, including his support of the Keystone XL oil pipeline. His frustration with the Trump administration, however, has brought him more in line with colleagues to his left.

His maternal grandparents were Jews who fled the Warsaw Ghetto, moving their family out of Poland to Mexico and eventually to New York. (Mr. Bennet’s parents raised him with Jewish and Christian traditions.)

His younger brother, James Bennet, is the editorial page editor of The New York Times. James Bennet recused himself on Thursday “from any work generated by the opinion desk related to the 2020 presidential election,” The Times said in a statement.

After stints as an aide to the Ohio governor and as counsel at the Justice Department, Michael Bennet came to Colorado, where he took a job with the Anschutz Investment Co., restructuring corporate debt. He later joined the administration of Mr. Hickenlooper, then the mayor of Denver, and spent several years as the superintendent of Denver Public Schools.

He lives in Denver with his wife, Susan Daggett, a natural resources lawyer, and their three daughters.

In January, after his impassioned speech on the Senate floor, Mr. Bennet went on MSNBC, where he was asked if he was considering a run for president. “I’m thinking about it,” he said, adding that he thought the nation was moving in a “terrible direction.”

“Donald Trump is much more a symptom of our problems than he is the creator of our problems,” the senator said. “He is an accelerant. He was sent here to blow this place up. That’s what people in my state who voted for him said. And guess what? They succeeded. But now we’ve got to pick up the pieces.”