While he has run unsuccessfully for local and state office three times before, Mr. Bryce, a union activist, has been endorsed by the Democratic Congressional Campaign Committee this time around. He raised $2.7 million through the end of 2017, according to the Federal Election Commission.
The most prominent conservative challenger to Mr. Ryan has been Paul Nehlen, a white nationalist and anti-Semite who challenged Mr. Ryan in 2016 and lost by 68 points. He raised $166,000 in 2017, according to the Federal Election Commission.
He is opposed to free trade, has called for deporting all Muslims from the United States, and wants the government to fortify the border “every step of the way from the Gulf of Mexico to the Pacific Ocean,” according to a statement on Wednesday.
In February, he was suspended from Twitter after he posted a racist image of Meghan Markle, the American fiancée of Britain’s Prince Harry. The Republican Party of Wisconsin cut ties with him shortly thereafter; a state party spokesman said he had “no place in the Republican Party.”
Also running for the Democratic nomination: Cathy Myers, a schoolteacher and member of the board of the Janesville school district. Like Mr. Bryce, she supports a long list of liberal policy positions, including gay and transgender rights, gun control and universal health care.
But she has chafed at Mr. Bryce’s media attention and relative fame. When he secured the support of the party’s congressional campaign committee, she criticized Mr. Bryce as a Washington insider, saying in a statement that “progressives in Wisconsin don’t need folks on the coasts to tell them what’s best for them.”
Ms. Myers raised $265,000 through the end of 2017, according to the Federal Election Commission.
A first-time candidate running for the Republican nomination, Mr. Polce is a former Army Green Beret and local businessman who has received little attention compared with other candidates. He supports building a wall on the Mexican border and opening up parts of Social Security and Medicare to the free market.
He raised nearly $18,000 through the end of 2017, according to the Federal Election Commission.