With the partisan emotions on both sides — Mr. Trump’s supporters see a plot to undermine his presidency, and Mrs. Clinton’s supporters see a conspiracy to keep her from the presidency — the result is an environment in which even those basic facts become the basis for dispute.

Mr. Trump’s team lashed out at the agencies after The Washington Post reported that the C.I.A. believed that Russia had intervened to undercut Mrs. Clinton and lift Mr. Trump, and The New York Times reported that Russia had broken into Republican National Committee computer networks just as they had broken into Democratic ones, but had released documents only on the Democrats.

For months, the president-elect has strenuously rejected all assertions that Russia was working to help him, though he did at one point invite Russia to find thousands of Mrs. Clinton’s emails. There is no evidence that the Russian meddling affected the outcome of the election or the legitimacy of the vote, but Mr. Trump and his aides want to shut the door on any such notion, including the idea that Mr. Putin schemed to put him in office.

Instead, Mr. Trump casts the issue as an unknowable mystery. “It could be Russia,” he recently told Time magazine. “And it could be China. And it could be some guy in his home in New Jersey.”

The Republicans who lead the congressional committees overseeing intelligence, the Pentagon and the Department of Homeland Security take the opposite view. They say that Russia was behind the election meddling, but that the scope and intent of the operation need deep investigation, hearings and public reports.

One question they may want to explore is why the intelligence agencies believe that the Republican networks were compromised while the F.B.I., which leads domestic cyberinvestigations, has apparently told Republicans that it has not seen evidence of that breach. Senior officials say the intelligence agencies’ conclusions are not being widely shared, even with law enforcement.