But in the case of Mr. Trump, his party controls the Senate, and it is not a stretch to envision Republicans providing the votes to throw out the articles, short-circuiting the process and sparing Mr. Trump an extended examination of his conduct.

Senate Republicans essentially laid out that scenario in background guidance circulated over the weekend, noting that a motion to dismiss the articles would be allowed under impeachment rules, and that such a vote took place during the Clinton trial after opening arguments and limited questioning by senators.

The tactic looms as a delicate proposition for Mr. McConnell and his Republican colleagues. First, they must mollify a mercurial president and Republican voters who will no doubt be incensed at the very idea of a Senate trial giving credence to the accusations that Mr. Trump improperly sought foreign help against a political rival. At the same time, they would need to demonstrate to the public that the Senate was taking its constitutional responsibilities seriously and not dismissing the House action out of hand.