In a statement, Van Hollen framed his candidacy as a response to voters' demand for change. "In this election, the American people called for change. They called for a change from Donald Trump's disastrous policies — but even bigger than that, a change from the status quo that isn't working for working people," he said.

Van Hollen's decision follows a push by grassroots progressives and some newly elected Democratic senators to draft him for the role, as members of the caucus seek an alternative to Schumer. "It's now on us to meet this moment, and to do that we need new leadership. This is not about any one person — it's about answering the call of the American people. That is why I'm running for Senate Majority Leader," he added.

Schumer, who has led the Senate Democratic caucus since 2017, remains favored to keep his position. Still, Van Hollen's challenge is likely to be the most serious Schumer has faced for the job. Democratic senators will hold a closed-door vote in December to choose their leadership for the next Congress; a simple majority of the caucus is required.

In an interview with MS NOW on Thursday night, Van Hollen said more than 10 senators have pledged to support him. "We have a lot of people, but here's the thing about an election like this: As you say, I'm the underdog," he said. "I told people I was thinking about it, and so now we are opening up the process, right? Now people will have to make a decision, one way or the other, and they have to decide whether they want to vote for change or whether they want to vote for the status quo."

Van Hollen plans to campaign on having the new Democratic majority use every available tool to end the Iran war, starting with the upcoming government funding measure to avoid a December shutdown, according to his team. He is also proposing to reverse President Donald Trump's "big, beautiful bill," get money out of politics and tackle corruption.

At 67, Van Hollen is newer to Congress than Schumer, 75, but both men have served for decades. Van Hollen was first elected to the Senate in 2016 after serving in the House since 2003. Schumer was first elected to the House in 1980 and moved to the Senate in 1999.

Schumer responded to Van Hollen's announcement on X, asserting he has the votes to win. "I welcome any discussion about the future of our caucus and the important work ahead. I'm proud of what we've accomplished together—55 seats and counting is an amazing result—and I have the votes to continue serving as Democratic Leader," he said. "I look forward to leading our new Democratic majority and delivering for the American people."

Sen. Bernie Sanders, I-Vt., said Wednesday that he would support Van Hollen if he launched an official bid. The day before, Sanders had said he would not back Schumer, telling a press conference that "in my view, the time is now for change."

Sen.-elect Abdul El-Sayed of Michigan endorsed Van Hollen shortly after the announcement Thursday night, writing on X, "I called on Sen. @ChrisVanHollen to lead our caucus as a candidate back in April because he leads with courage and experience. We need both right now. Which is why I'm proud to stand with him in his bid to lead our Senate majority." El-Sayed added that to "earn our mandate," Democrats "will require bold leadership."

Still, Schumer has maintained support from longtime colleagues who credit his work as minority leader ahead of Democrats' midterm victories. "Chuck Schumer is one of the principal architects of the most successful election in modern history, and I see no reason to change the leadership that helped make that success possible," Sen. Angus King, I-Maine, said in a statement Thursday night. "Why would you fire the manager when you just won the World Series?" King said Schumer "outlined an aggressive plan for the new Democratic majority which is directly responsive to the message we heard from the voters, and he has the experience and unique mastery of the Senate process to make it happen."

Sen. Kirsten Gillibrand, D-N.Y., also urged Democrats earlier this week not to turn their backs on Schumer, saying "no one has put in the time and effort that anyone has put into this cycle than he did." Gillibrand, who oversaw Senate Democrats' campaign arm for the midterms, said Schumer ensured resources were provided to help 100,000 new voters register in Mississippi, where Sen.-elect Scott Colom just captured a stunning victory. "That takes vision. It takes clarity of thought. It takes strategic leadership, and that is what Sen. Schumer has done, and that's why you will see, despite all the grumblings, enormous gratitude for the hard work he has done to get us to this position," she said.

The leadership vote will test whether Democrats, fresh off a strong midterm showing, opt for continuity or a new direction as they prepare to take the majority.