Senate Democratic leader Chuck Schumer is facing a potentially serious challenge to his hold on power as momentum builds behind Chris Van Hollen, with the Maryland senator now reportedly open to a run for majority leader.

A movement to draft Van Hollen to challenge Schumer is gaining steam, according to Politico Playbook, which reported Monday that two people close to the effort said it was underway.

A person familiar with Van Hollen’s thinking told the outlet that the senator has “received an outpouring of calls and is now in active listening mode.”