Because Democrats are forcing the vote under the War Powers Act, they only need a simple majority for it to pass. With every Democrat expected to support it, it is expected to pass the Senate on Thursday. If the resolution reaches Trump's desk, he is all but guaranteed to veto it, and the Senate is not expected to be able to override the veto.

Kaine estimated that in addition to the GOP senators who were already on board with the resolution, roughly an additional five to seven could be viewed as potential "yes" votes on his resolution.

She initially told KTOO, an Alaskan radio station , last month that she has not made a final decision, but “my inclination right now is, I’m hesitant to sign on to it for a host of different reasons.”

However, she also told reporters last week that Congress needed to do more to exert itself against the executive branch, and noted that the war powers debate was coming up.

"I think the path forward is for the legislative branch is to wake up and get its act together … assert your own powers," Murkowski said. "We're going to have a debate coming up on war powers. That's legitimate for us as a Congress to discuss and debate."