Then U.S. President Barack Obama and President-elect Donald Trump meet in the Oval Office of the White House in Washington on Nov. 10, 2016. (Michael Reynolds / EPA)

Donald Trump’s absurd accusation that Barack Obama wiretapped his telephones “during the very sacred election process” is a depressing reminder that a president who has access to the resources of the nation’s intelligence agencies prefers to believe conspiracy theories.

Even more depressing than Trump’s weekend tweetstorm was what followed: his staff trying to justify his outburst, and some Republicans — including House Intelligence Committee Chairman Devin Nunes (R-Tulare) — indulging the president in his attempt to shift public attention away from persistent questions about his campaign’s ties to Russia and onto a supposed plot against him by the Obama administration and the intelligence bureaucracy. That could introduce even more friction into congressional investigations of Russian interference in last year’s presidential election, which already have been strained by partisanship.

Nunes said that his panel’s investigation would also include "inquiries into whether the government was conducting surveillance activities on any political party’s campaign officials or surrogates." That sounds as if the allegation is based on serious reports of illegal politically motivated surveillance of a political campaign, which would be a scandal comparable to Watergate. But where is the evidence of such abuse?

Trump’s sensational assertion that Obama ordered the tapping of telephones at Trump Tower “just before the victory” has been denied by Obama and former Director of National Intelligence James R. Clapper. Multiple news organizations have reported that FBI Director James B. Comey asked the Department of Justice to publicly repudiate Trump’s claim. Finally, there is the inconvenient fact that presidents don’t order wiretaps.

So where did Trump get the idea that Obama wiretapped him? The best explanation seems to be that he was inspired by a report in Breitbart News, which itself cited a commentary by radio host Marc Levin in which he urged Congress to investigate Obama’s “silent coup” against Trump.

The Breitbart story also linked to stories in other publications about an order supposedly issued by the Foreign Intelligence Surveillance Court for inspection of a computer server at Trump Tower in connection with an investigation of Russian banks. But even the author of the original report about the supposed court order says that she never wrote that it included authorization for a wiretap. (The Washington Post’s fact-checker has cast doubt on these reports, and gave Trump the dreaded “Four Pinocchios” rating for his wiretapping claim.)

Trump’s reckless accusation is inseparable from his longstanding view that concerns about Russian meddling in the election are raised in an effort to delegitimize his presidency. In fact, one can denounce Russian interference and still acknowledge Trump as the winner of the election — provided, of course, that his campaign wasn’t involved in Russian efforts to sabotage Clinton’s prospects. And so far there is no evidence of that. Clapper said over the weekend that he had no knowledge of evidence that Trump’s campaign colluded with the Russians.

But it is in the president’s interest, as well as the nation’s, to put to rest suspicions about any such collusion if they are untrue. That is why it is imperative that the Senate and House intelligence committees expedite their investigation of possible contacts between the Trump campaign and Russian intelligence, perhaps coordinating their investigations to avoid duplication. Other aspects of the investigation can wait until this matter is resolved.

For the congressional investigation to be credible, it must be bipartisan. That means Democrats must be willing to refrain from using it to score extraneous points against a president who is deeply unpopular with their base, and Republicans must be willing not to endorse or acquiesce in outrageous allegations such as the wiretapping charge.

Meanwhile, if the president expects to be treated fairly he will stop the baseless attacks on others — including his predecessor.