Ever since President Trump tweeted, in the early morning of March 4th, that “Obama had my ‘wires tapped’ in Trump Tower just before the victory,” the White House and its defenders have labored to find a justification for the false allegation. After two false starts, the White House is trying out another claim this week: Susan Rice, President Barack Obama’s national-security adviser, did it. This third swing at justifying Trump’s tweet is as bogus as the first two.

The first effort to defend Trump took his tweet literally and rested on thinly sourced reports that the FISA court may have issued a warrant that authorized spying on him. This claim was debunked by every official in a position to know the truth.

“If you take it literally, it didn’t happen,” Devin Nunes, the chairman of the House Intelligence Committee, told me two weeks ago.

James Clapper, the Obama Administration’s director of national intelligence, denied Trump’s allegation in an interview with NBC News the day after Trump’s tweet. “For the part of the national-security apparatus that I oversaw as D.N.I., there was no such wiretap activity mounted against the President-elect at the time, or as a candidate, or against his campaign,” he said.

James Comey, the head of the F.B.I., confirmed Clapper’s assessment during testimony before Congress, on March 20th. “With respect to the President’s tweets about alleged wiretapping directed at him by the prior Administration, I have no information that supports those tweets, and we have looked carefully inside the F.B.I.,” Comey said. “The Department of Justice has asked me to share with you that the answer is the same for the Department of Justice and all its components. The department has no information that supports those tweets.”

Strike one.

In a second, overlapping attempt to justify Trump’s claim, the White House press secretary, Sean Spicer, repeated a false statement by a Fox News pundit, Judge Andrew Napolitano, at a press briefing on March 15th. The day before, Napolitano had claimed that Obama “didn’t use the N.S.A., he didn’t use the C.I.A., he didn’t use the F.B.I., and he didn’t use the Department of Justice; he used G.C.H.Q.”—Government Communications Headquarters, the intelligence service of the United Kingdom.

Trump shrugged when asked about Spicer’s remark at a press conference with the German Chancellor, Angela Merkel, later that week. “We said nothing,” Trump insisted. “All we did was quote a certain very talented legal mind who was the one responsible for saying that on television. I didn’t make an opinion on it. That was a statement made by a very talented lawyer on Fox. And so you shouldn’t be talking to me, you should be talking to Fox, O.K.?”

Once again, everyone in a position to know denied the claim. “Recent allegations made by media commentator Judge Andrew Napolitano about GCHQ being asked to conduct ‘wiretapping’ against the then president-elect are nonsense,” the UK’s Government Communications Headquarters said in a rare public statement. “They are utterly ridiculous and should be ignored.”

Michael Rogers, the director of the N.S.A., which has an important intelligence-sharing agreement with G.C.H.Q. and three other countries that is known as Five Eyes, also disavowed the claim. “Did you ever request that your counterparts in G.C.H.Q. should wiretap Mr. Trump on behalf of President Obama?” Adam Schiff, the ranking member of the House Intelligence Committee, asked Rogers at the March 20th hearing.

“No, sir, nor would I. That would be expressly against the construct of the Five Eyes agreement that’s been in place for decades,” Rogers responded.

Even Fox News seemed embarrassed by Spicer and Trump’s statements. “Fox News knows of no evidence of any kind that the now-President of the United States was surveilled at any time, in any way,” Shep Smith, one of the network’s anchors, said shortly after Trump’s press conference. Napolitano was reportedly suspended from the network over the false claim, though when he returned to the air last week, he repeated it.

Strike two.

On March 20th, the same day that these first two claims were definitively rejected by Nunes, Comey, and Rogers, the White House and some Republicans started to coördinate a third attempt to justify Trump’s tweet: Trump was monitored through the use of so-called incidental collection and unmasking.

The coördination was obvious. White House officials started to raise the issue of incidental collection with reporters, including me. Almost every Republican at the March 20th Intelligence Committee hearing asked Comey and Rogers about it. Spicer began emphasizing the issue at White House briefings. And speaking with reporters after the Intelligence Committee hearing, Nunes hinted at the coming public-relations campaign. “The White House believes other surveillance activities were used,” he said. “We don’t have evidence of that yet, but we can’t rule it out.”

Two days later, Nunes was brought to the White House to see intelligence reports that allegedly included the names of Trump associates. After an outcry, Schiff received the same briefing. Nunes said he was alarmed at the presence of the names, but he also said that there was nothing in the reports related to Russia and that there was nothing illegal that occurred.

The scandal now is supposed to be that the names of Trump associates made it into these reports at all. The N.S.A., whose main job is signals intelligence—tapping phones and intercepting e-mail and other kinds of electronic communications—has wide latitude to legally spy on foreigners. But oftentimes foreigners are talking to or about Americans, who are not legal targets of N.S.A. surveillance. The agency has safeguards to protect the privacy of those Americans who are incidentally swept up in the legal surveillance of foreigners.

As Rogers explained in his March 20th testimony, the first step is to determine whether the intercepted communication has “intelligence value.” He said, “We’ll ask ourselves, is there criminal activity involved, is there a threat, potential threat or harm to U.S. individuals being discussed in a conversation?” If the N.S.A. determines that the information doesn’t have value, it purges the data. If it determines that it does, it masks the identity of the Americans before circulating the intelligence. If a policymaker wants to unmask the identity of a redacted name that she comes across in a report, so she can better understand the intelligence, she can make that request to the N.S.A.

Yesterday, several right-leaning outlets reported that some of the materials shared with Nunes and Schiff showed that Susan Rice made unmasking requests that revealed the identities of Trump associates. This news is being treated as a full-blown intelligence scandal on conservative talk radio and Fox News. Naturally, Trump tweeted about it and Spicer emphasized the news during his briefing.

There are valid reasons to be concerned about unmasking. Civil libertarians have long feared that spy agencies could use the legal targeting of foreigners as a back door to spy on Americans with whom they are communicating. That’s why there is an audit trail and a legal process in place for making unmasking requests.

Rogers said that the N.S.A. uses a two-part test to evaluate unmasking requests: “Is there a valid need to know in the course of the execution of their official duties?” and “Is the identification necessary to truly understand the context of the intelligence value that the report is designed to generate?”