Ohio Democratic Rep. Tim Ryan on Thursday became the first lawmaker to formally challenge House Minority Leader Nancy Pelosi for her post, a move that comes as the California power-broker faces growing unrest inside the Democratic caucus in the wake of last week’s election.

Ryan, who had been publicly considering mounting a leadership bid for days, announced his decision in a letter to colleagues.

He said he was “disheartened” by the election results and Democrats “must not let this opportunity for change pass by without a fight.”

Ryan wrote: “Over the last 18 years, Democrats have only been in the majority of the House of Representatives for two terms and last week’s election results set us back even further. We have lost over 60 seats since 2010. We have the fewest Democrats in state and federal offices since Reconstruction. At this time of fear and disillusionment, we owe it to our constituencies to listen and bring a new voice into leadership.”

Pelosi last faced a challenge in 2010 after the party’s midterm clobbering that cost them the House. Then-Rep. Heath Shuler, D-N.C., ran and only got 43 votes.

But Pelosi is dealing with a fluid and unpredictable situation on Capitol Hill. Democrats earlier this week delayed leadership elections until Nov. 30, amid consternation over the party’s failure to win control of either chamber of Congress on Election Day.

Angry Democratic lawmakers expressed their frustration in a closed-door session Thursday, and some grew angrier after Pelosi left the room to hold her weekly news conference, according to those who attended the session. Some also were offended she handed out a legislative plan for next year, suggesting she should be listening to members rather than forging ahead and flexing her muscle.

“Some of her supporters are tone-deaf,” one Democratic member groused.

Pelosi has remained confident of her support within the caucus, saying at a press conference Thursday she has support of at least two-thirds of the Democratic members -- and that’s “without having asked for their vote yet.”

"When somebody challenges you, your supporters turn out, both internally in the caucus and in the country," Pelosi said.

Ryan, in his letter, called for creating “America 2.0 --- a multicultural, progressive, and innovative country that fights every day for ordinary people.”

Before making it official, Ryan told Fox News it was time “for a new direction, a new way of doing business, a new Democratic Party.”

“We have to talk to those people who take a shower after work, not those who just take a shower before work,” Ryan said.

Overall, the math still appears to favor Pelosi.

Democrats will have about 198 members in their caucus, meaning the successful candidate for leader needs 100 votes.

It’s unclear whether any other candidates may emerge to challenge Pelosi.

Earlier, Fox News was told some House Democrats were pushing House Democratic Caucus Vice Chairman Joe Crowley, D-N.Y., to run. Crowley, who is from working-class Queens and has broad support inside the caucus, was seen as a possible choice to topple Pelosi.

However, Crowley announced late Thursday he’s running for chairman of the House Democratic Caucus.

On Wednesday, Pelosi; House Minority Whip Steny Hoyer, D-Md.; and Assistant Minority Leader Jim Clyburn, D-S.C., all announced bids for their old positions.

Fox News’ Chad Pergram and The Associated Press contributed to this report.