President Trump enters the Oval Office. (Erik S. Lesser/European Pressphoto Agency)

ALL PRESIDENTS enter the White House with a store of credibility that comes with the office, which they can use to press an agenda, move Washington’s policy machinery or lead the nation when crisis strikes. President Trump is burning through his with breathtaking speed. That will ultimately hurt him, the presidency and the country.

His latest rash expenditure from his already depleted trust account came in yet another Twitter outburst, in which Mr. Trump accused President Barack Obama of having his phones at Trump Tower tapped during the 2016 campaign. As is so often the case, Mr. Trump offered no substance to back up his charge, which appears to rely on a handful of news stories containing no significant evidence the former president personally ordered any wiretapping, let alone of Mr. Trump.

For some time, there have been suggestions that the Foreign Intelligence Surveillance Court, which operates behind closed doors, issued a warrant allowing federal agents to examine potential contacts between Trumpworld and Russia. But The Post and others have not confirmed these reports, and none of them personally implicate Mr. Obama. Nor would they: The president cannot order wiretaps. According to U.S. officials cited by The Post and others, FBI Director James B. Comey has asked the Justice Department to publicly knock down Mr. Trump’s allegations.

Mr. Trump has nevertheless asked Congress to investigate his accusations. To which we say: fine, as long as doing so serves congressional investigators’ larger purpose. The intelligence community has united around the conclusion that the Russian government interfered with the country’s democratic process, and that the interference was tilted toward helping Mr. Trump. The nation must know what methods the Russians used, why they acted, to what extent any Americans wittingly or unwittingly aided them, and how to combat future intrusions.

In the process of answering these central questions, it would be only natural for the Senate Select Committee on Intelligence, many of whose members are committed to conducting a serious investigation, to inquire about any foreign intelligence surveillance relating to Mr. Trump and Russia, as well as the suspicions on which any warrants might have been based. As long as lawmakers see that a judge authorized any direct surveillance of Mr. Trump, his circle or his property, they can quickly discard concerns about improper wiretapping and reassure the public about federal officials’ propriety. After all, Mr. Trump asked. He may not like the answer he gets back.

If anything, the “Towergate” episode underlines the importance of a fair and thorough investigation into how and why a hostile foreign power meddled in the most fundamental process of American democracy. As the controversy continued to unfold Monday, Trump spokeswoman Sarah Huckabee Sanders said on “Good Morning America” that the president wants the House Intelligence Committee to examine his allegations against Mr. Obama. This is yet another warning sign about the direction of the House panel’s work, which, under the leadership of Chairman Devin Nunes (R-Calif.), already appears to be poisoned with partisanship. It would be better for the House to run no investigation than to conduct a slanted one.

Meanwhile, the members of the Senate panel still have the credibility to proceed, even as Mr. Trump and his enablers lose more and more by the hour.