Dr. Abdul El-Sayed, a progressive former public health official from Ann Arbor, joined the Michigan Senate race on Thursday, casting himself as a populist fighter eager to mount a muscular opposition to the Trump administration.

Dr. El-Sayed, a former health director in Wayne County, Mich., who ran unsuccessfully for governor in 2018, is the latest entrant into a Democratic primary field that is likely to be crowded and competitive. Democrats are hoping to retain the seat, now held by Senator Gary Peters, who is retiring.

“We need to break the chokehold that billionaires and oligarchs like Donald Trump and Elon Musk have on our politics and economy,” he said in a statement as he announced his candidacy. “It’s not just about what we’re fighting against. It’s about what we fight for.”

Yet even as he name-checked his policy goals around the economy, the environment and guaranteed health care, Dr. El-Sayed, 40, also made clear this week that he hoped to tap into the fury of Democrats who are horrified by President Trump’s actions and frustrated with their party’s inability to curb his powers.

“They want somebody who can take the fight openly, honestly and clearly and directly to Trump and Musk, but also somebody who can build from the wreckage that they leave behind,” he said in an interview, alluding in part to Mr. Musk’s efforts to gut the federal government.

Of course, Republicans control the House and the Senate, and Democrats in Washington are severely limited in their ability to rein in the majority party, much less advance their own agenda.