Senate Democrats are preparing to take power in January with a larger-than-expected majority, but a leadership contest is threatening to overshadow their early planning.

Maryland Sen. Chris Van Hollen announced Thursday night that he will challenge longtime Democratic leader Chuck Schumer, setting up a secret-ballot election and a pressure campaign aimed at senators who have avoided taking a public position.

“People will have to make a decision one way or the other,” Van Hollen said in an MS NOW interview after his announcement.

The contest comes as Democrats begin discussing their agenda for their first days in the majority. Some are now considering whether to move leadership elections up to next week to avoid a prolonged fight, according to two people familiar with private discussions. Otherwise, the vote is scheduled for Dec. 1.

Schumer appears to retain the advantage. Several senators have publicly pledged their support, while others have privately told POLITICO they back him. On Thursday night, Schumer said, “I have the votes to continue serving as Democratic Leader.” Sens. Catherine Cortez Masto and Jacky Rosen of Nevada and Angus King of Maine also publicly endorsed him.

Van Hollen acknowledged that he is the “underdog” but said he has secured more than 10 commitments among the 55 Democrats expected to vote. That number would rise to 56 if Mary Peltola holds her lead in Alaska.

Sen. Bernie Sanders of Vermont and Michigan Sen.-elect Abdul El-Sayed endorsed Van Hollen after his announcement. The Maryland senator also encouraged viewers to contact senators, saying Americans want “a little bit more democracy in the Senate Democratic Caucus.”

Leadership questions are also emerging elsewhere on Capitol Hill. Rep. Janelle Bynum of Oregon is urging House Democrats to select subcommittee leaders based on merit rather than seniority alone. Her proposal offers a narrower alternative to Nevada Rep. Susie Lee’s call for a four-term limit on full committee chairs.

Among Senate Republicans, Kansas Sen. Jerry Moran is pursuing the top GOP position on the Appropriations Committee, potentially leapfrogging the more senior Lisa Murkowski of Alaska. Moran has until early January to decide whether to force a vote among Republican appropriators; the full GOP conference would then decide whether to accept their choice.