Senator Chris Van Hollen of Maryland said he will run for Senate majority leader, a challenge to Senator Chuck Schumer of New York, according to Politico's live report on the announcement. Politico described the move as a setback for Schumer, a longtime Democratic leader, and said he "remains favored to win."

According to The New York Times, Van Hollen has emerged as a favorite of Democrats seeking an alternative to Schumer, who says he has the votes to win.

Axios reported that Van Hollen announced the challenge on Thursday. Its summary said the bid gives grassroots activists nearly three weeks to pressure Senate Democrats before they cast secret ballots in the Dec. 1 leadership election. Axios also wrote that the attempt to oust Schumer, D-N.Y., underscores "deep divisions" plaguing the Democratic Party.

The reports differ on Schumer's standing. Politico said he remains favored, while The New York Times reported his own claim that he has the votes to win. None of the three summaries gives a vote count, and the reports do not say which senators have committed to either candidate.

Under the timeline Axios described, the leadership question will be settled by the secret ballot on Dec. 1, according to the reports available so far.

Sources: Politico: Chris Van Hollen says he will run for Senate majority leader; The New York Times: Chris Van Hollen Set to Challenge Chuck Schumer for Senate Majority Leader; Axios: Chris Van Hollen to challenge Schumer for Senate majority leader.