(CNN) Senate Minority Leader Chuck Schumer said Sunday night he is prepared to "force votes for witnesses and documents" in the Senate impeachment trial if Senate Majority Leader Mitch McConnell does not call for it in his proposal.

"We have the right to do it, We are going to do it and we are going to do it at the beginning on Tuesday if leader McConnell doesn't call for these witnesses in his proposal," Schumer said at a press conference in New York. "We're allowed to amend it, and ask for them. I am allowed to amend it -- and then if they say well let's wait and hear the arguments we'll want a vote after they hear the arguments as well and we will do everything we can to force votes again."

Schumer's comments come as the Senate impeachment trial is set to begin in earnest Tuesday when Republicans and Democrats are expected to battle over a resolution setting the rules for the trial and shortly after start opening arguments. McConnell has said he doesn't want the Senate to debate the questions of compelling witnesses and documents until after opening arguments and questions are completed.

Fifty-one senators would have to vote for witnesses, so if all 47 Democrats are unified, four Republicans would need to support it to pass. It's still an open question if Democrats can wrangle four Republicans to break ranks.

"And it will be up to four Republicans to side with the Constitution, to side with our Democracy, to side with rule of law," Schumer told reporters. "And not side, in blind obeisance, to President Trump and his desire to suppress the truth. Because in my judgment, he probably thinks he's guilty."

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