President Donald Trump made a deeply troubling claim this weekend: His predecessor illegally ordered a wiretap of his phones at Trump Tower. He cited not one bit of evidence to support the charge made Saturday morning on his personal Twitter account.

Maybe Trump knows that accusing former President Barack Obama of a felony, as well as of subverting the democratic process, is preposterous. But perhaps his inability to stop revelations that the Russian government interfered in the 2016 election and sought to cozy up to his campaign team made Trump repeat some fake news to shake things up.

Whatever Trump’s motivation, the resulting tremors are all quite real.

Trump doubled down Sunday by demanding that Congress investigate Obama. In so doing, he has now tied existing probes by national security agencies, the FBI and the House and Senate intelligence committees of Moscow’s meddling in the election directly to claims that his campaign had any back-channel contacts with the rival superpower.

The Republican-controlled Congress, which has shown little inclination to use its oversight authority, now has no excuse to dawdle. Trump’s charge goes to the very integrity of our government, our rule of law.

Obama, through a spokesman, denied ordering any surveillance. It would be illegal to do so. The Fourth Amendment requires prosecutors to present evidence to a court that a crime was committed, and a 1968 federal law spells out the guidelines. If the Justice Department sought to gather intelligence because of suspected espionage or terrorism, first it would have to seek a warrant under the Foreign Intelligence Surveillance Court Act.

There is a process. There are checks and balances.

If either criminal activity or spying were going on at Trump Tower, that would be one heck of a story. But when James Clapper, the former director of national security, was asked on NBC’s “Meet the Press” whether a FISA order existed, Clapper flatly declared, “I can deny it.” FBI Director James Comey wants the administration to deny the existence of any wiretaps, but it is refusing to do so.

The White House yesterday declined to provide the specific basis for Trump’s claim. Some White House representatives suggest the president had access to intelligence information. Press Secretary Sean Spicer refused to discuss Comey’s position, saying, “If we start down the rabbit hole of discussing this stuff, we end up in a very difficult place.”

Too late. We are already in that very difficult place. Trump should let Comey make a statement. If not, then the Senate Intelligence Committee should bring the FBI director in for questioning; the GOP had no qualms about doing so when the subject was Hillary Clinton and her emails.

Trump can ask his own national security officials whether there is or was any surveillance at Trump Tower. He should seek to have the information released, if not publicly, then to members of Congress with the proper security clearances.

GOP Sen. Ben Sasse of Nebraska said Trump’s charge has put the United States “in the midst of a civilization-warping crisis of public trust.” He’s right. The American people deserve to know the truth about what the heck is going on. — The editorial board