This month, President Trump threw out a major, unfounded allegation about former president Barack Obama without much explanation of what he’s actually charging Obama did. The gist of the allegation is that before he left office, Obama’s administration committed some sort of crime to undermine Trump’s presidency. #Obamagate, he called it, in a tweet on Mother’s Day and several since.

Trump is keeping his allegation intentionally vague. "You know what the crime is,” he said when asked by reporters what specific crimes he was alleging. Pressed, Trump was unable to name any.

But we got some clues recently that “Obamagate” may be connected to two things close to Trump’s heart:

  1. Trump’s full-scale effort to undermine the Russia investigation that dominated nearly the first two years of his presidency and swept up many of his top aides, including former national security adviser Michael Flynn.
  2. Trump’s reelection efforts

Whatever it is, this allegation ramped up last week with the help of some Senate Republicans, Trump’s conservative media allies and his top intelligence chief — and more and more, it seems to be geared at Trump’s presumptive 2020 opponent, Joe Biden. But a key part of the allegation received a big blow this week. Let’s explain, step by step.

After tweeting about what President Trump called "Obamagate," Trump was unable to name which specific crime he was accusing his predecessor of having committed. (Reuters)

Last week, Senate Republicans released the names of Obama administration officials who may have asked intelligence officials to reveal the hidden names of Americans popping up in intelligence reports from November 2016 to January 2017. One of the people on the senators’ list was then-Vice President Biden.

Republican senators alleged that an American unmasked in one of those intelligence reports was Flynn, who was picked up in FBI intelligence as talking to the Russian ambassador about sanctions levied on Russia by the Obama administration. But new reporting by The Post’s Ellen Nakashima suggests that’s not true: Flynn’s name was not even redacted in FBI intelligence reports, so there would have been no need to request to unmask him. In addition, the list the NSA provided to Republican senators did not include this FBI summary about the Flynn-Russia ambassador call.

(At the time of the call, Flynn was the incoming national security adviser, but Trump hadn’t been inaugurated yet. It was lies about those conversations that eventually got Flynn fired from his job shortly after Trump was inaugurated, and eventually led to a guilty plea that the Justice Department is now arguing wasn’t actually a crime.)

In another blow to Republicans’ case that Flynn was improperly unmasked by Obama officials, intelligence agencies routinely respond to such “unmasking”requests, which reveal the identities of U.S. individuals who are referred to in documents to allow government officials to better understand what they are reading. Unmaskings are legal and agents say it’s a useful tool to uncover potential spies, according to The Post’s Shane Harris and Matt Zapotosky.

By contrast, sharing the names of those who request the unmasking is rare.

Republican senators received this unmasking list through a chain of events: Trump’s acting director of intelligence, Richard Grenell, declassified them and gave the Justice Department their names, which gave them to GOP senators at their request, who publicized them. And these senators seemed to be asking: Did Biden somehow play a role in getting the FBI to investigate one of Trump’s allies?

Trump connected those dots, alleging that because Biden’s name appears on the list of people who requested to unmask Flynn, “he knew everything about it.” “This was all Obama. This was all Biden,” he said in an interview with Fox Business.

There’s no evidence that’s the case, and it’s especially less so given we now know that the list Republicans are sharing didn’t even include an unmasking request for the Flynn call in question.

Trump has long been focused on the FBI’s involvement in the early months of his presidency-elect and presidency. Since his taking office, the president and his allies have accused the investigation into Russian interference in the 2016 election and any possible ties to the Trump campaign as being a “hoax” and a political effort to undermine his presidency. Four years later, Trump and others continue to question the motives behind the investigation and the Obama administration’s role in it -- especially Biden’s, now that he’s Democrats’ presumptive nominee.

“It is, from my standpoint, pretty curious that the vice president of the United States would be requesting unmasking in this case of General Flynn eight days before he left office,” Sen. Ron Johnson (R-Wis.), the chair of the Homeland Security Committee and one of the senators who released the names, said on Fox News after releasing the names. (Again, based on the list Johnson publicized, the specific unmasking request about Flynn’s call with the Russian ambassador didn’t happen.)

That question has galvanized the right, as Trump continues to get low marks from the public for his response to the coronavirus pandemic. Conservative blogger Erick Erickson, who has criticized Trump’s coronavirus response, joined in by alleging on his blog that “a lot of people close to the Obama Administration spent a year leaking information about Mike Flynn to the press."

Biden’s campaign called this a diversion from the coronavirus situation and emphasized that he did nothing wrong in requesting unmasking in intelligence reports. “The documents simply indicate the breadth and depth of concern across the American government, including among career officials, over intelligence reports of Michael Flynn’s attempts to undermine ongoing American national security policy through discussions with Russian officials or other foreign representatives,” his campaign said in a statement.

Biden also said he wasn’t aware of any criminal investigation into Flynn. The FBI investigation into Russian meddling-turned special counsel investigation-turned Mueller report was critical of Trump but declined to accuse him of obstruction of justice, citing Justice Department policy against indicting a sitting president. (Indeed, much of that happened after Biden was out of office.)

Why is Trump so focused on Flynn? Flynn was a central figure in the special counsel investigation. After he pleaded guilty to lying to the FBI and getting fired from his job as national security adviser, he struck a cooperation agreement to help investigators looked into Russian meddling in the election and whether the Trump campaign helped.

Trump has always bristled at Flynn and his allies being caught up in the investigation, alleging it was politically motivated to undermine his presidency shortly after it got started.

As recently as a few weeks ago, he said he’s open to pardoning Flynn. Though thanks to his Justice Department, he may not have to. Last week, the Justice Department under Attorney General William P. Barr moved to drop the case against Flynn, saying that essentially the FBI shouldn’t have been investigating Flynn in the first place and thus his lies weren’t material to a legitimate investigation. (A federal judge has put that on hold while he waits to hear from legal experts and a former judge who think Flynn should get sentenced.)

If Trump were trying to drum up another Ukraine-like scandal against Biden, this would be how it gets started. But just like with Biden’s work in Ukraine, when it comes to the Flynn investigation, there’s very little evidence that Biden did anything untoward, much less illegal.