WASHINGTON — Senator Mitch McConnell, the majority leader, called on Congress on Tuesday to move on from the Mueller report and issued his own verdict from the Senate floor: “Case closed.”

“With an exhaustive investigation complete, would the country finally unify to confront the real challenges before us?” Mr. McConnell said. “Or would we remain consumed by unhinged partisanship, and keep dividing ourselves to the point that Putin and his agents need only stand on the sidelines and watch as their job is done for them?”

“Regrettably,” he continued, “the answer is obvious.”

Mr. McConnell’s speech pointed up the profound gap between the Republican-controlled Senate and the Democrat-controlled House. House Democrats are locked in an escalating fight with President Trump, who is trying to slam shut House investigations of all sorts. The House Judiciary Committee is preparing to hold Attorney General William P. Barr in contempt of Congress on Wednesday for ignoring a subpoena for the full report of the special counsel, Robert S. Mueller III, and his underlying evidence.

The Treasury secretary, Steven Mnuchin, told the chairman of the House Ways and Means Committee, Richard E. Neal of Massachusetts, that he would not turn over six years of Mr. Trump’s personal and business tax returns, as demanded by Mr. Neal under the federal tax code. And on Tuesday, the White House instructed Donald F. McGahn II, the former White House counsel, to hold onto documents subpoenaed by House investigators because Mr. Trump might want to assert executive privilege over them.