Sen. Jon Tester (D-MT), one of the most vulnerable Democrats up for reelection, is under the microscope as Senate Majority Leader Chuck Schumer (D-NY) is expected to attempt to move to dismiss or table the two impeachment articles against Homeland Security Secretary Alejandro Mayorkas on Wednesday.

Once senators are sworn in as jurors Wednesday, the 51-member Democratic majority, which includes three independents who caucus with them, could dismiss or delay the trial if all Democrats can remain united. It remains unclear if Democrats will be united on motions to dismiss due to the fact that if there’s one Democratic defection, they would need at least one Republican vote to end the trial.