I think that if the House sends the House agreed articles of impeachment to the Senate then the Senate must accept them and must hold a trial.
But, Legal folk may argue on this
What's Next for President Donald Trump? Here's What Happens in a Senate Impeachment Trial
“There is no text in the Constitution that says the Senate must hold a trial,” Primus says. “[But] it is clear from the design of the Constitution that the Senate is supposed to hold the trial.”
Article I, section 2 of the U.S. Constitution says “the Senate shall have the sole Power to try all Impeachments…[but] no person shall be convicted without the Concurrence of two-thirds of the Members present.”
Some have argued that a senator could submit a motion to dismiss the charges against the President that would only need a simple majority to pass. Such a motion was introduced during the Clinton impeachment trial, and failed.
“I don’t think the Senate is likely to do that, and it’s an unresolved question if the Senate can do that,” Erwin Chemerinsky, the Dean of the University of California Berkeley School of Law, tells TIME.
I understand that the rules of the Senate trial are up to the Senate. But based on current goings on it seems the House can hold back passing on the articles until some conditions are agreed upon.
Anyway, its interesting to see how this goes down.
I'm finding it very weird how the Senate want to exclude witnesses and want to coordinate with the accused.