President Donald Trump spent his long Memorial Day weekend sequestered mostly in the White House. But instead of holiday tweeting about the “haters and losers”—of which, he once said, “sadly, there are many”—he opted to lob innuendo and unfounded accusations at the man who occupied the office before him.

Barack Obama, Trump declared over the course of several days, “did NOTHING” on trade, let the sanctioned Chinese phone company ZTE “flourish with no security checks,” employed various lawyers on special counsel Robert Mueller’s Russia probe, ignored Russian election meddling, and, above all, authorized “spying” on the Trump 2016 campaign.

Broadsides against his predecessor are nothing new for Trump. Nor are the false and misleading suggestions that President Obama snooped on him during his campaign. In early 2017, Trump very publicly, and erroneously, accused Obama of wiretapping him in 2016.

What stood out about the weekend’s salvo was the vitriol, perhaps panic, behind it and the frostiness it underscored about the relationship between the two most recent Oval Office occupants.

According to two White House officials, Trump has been privately wondering whether Obama is actively working behind the scenes to undermine or undercut his presidency. And he’s done so without bothering to pick up the phone to ask or confront his predecessor.

Obama and Trump have not spoken since the inauguration. There was an attempt. Following Trump’s inauguration, the new president tried to call Obama. But according to The Wall Street Journal, the two never connected. Matters weren’t helped when, in early 2017, Obama became furious about Trump’s groundless allegation that the former had wiretapped the latter in 2016.

There has been no communication since. When asked if Jan. 20, 2017, was the last time the two spoke, White House press secretary Sarah Huckabee Sanders told The Daily Beast, “as far as I know.”

The cold front has extended beyond the presidential level. According to one former senior Obama administration official, no one in the Trump White House has contacted top members of Obama’s national-security team to either inquire about or discuss the spying accusations.

“To my knowledge,” the senior official said, “none of those people are in contact with each other at a substantive level.”

Several of those members, including former Director of National Intelligence James Clapper and former CIA Director John Brennan, have been blistering in their criticism of Trump and, as a result, the routine subject of Team Trump’s missives. The result has been a vicious and petty war of words that would have been utterly discordant for any presidency prior.

“I think they are all at the point where they are offended by the attacks on the rule of law,” the senior official said of Clapper, Brennan, and the like. “Roger Stone told John Brennan he should take a cyanide pill. Once you get to that point it is hard to be offended. But they are deeply worried about the harm it is doing to our democracy.”

The most senior members of successive administrations usually adopt a muted approach to one another out of a sense of professional courtesy. That is particularly true at the presidential level, where there is a particular interest in demonstrating a continuity to the office. Obama has largely done his part, weighing in sporadically on the Trump presidency and almost exclusively during those occasions when his major policy achievements are being rolled back or unraveled.

Trump has declined to abide by such norms. In private conversation, he has repeatedly brought up Obama’s supposed “spying” right before his shock election victory, with one close confidant characterizing it as more often “musing than definitive” statement or a firm conviction that he’s uncovered the crime of the century. And yet, those musings often spill over into public, with the current president often comparing the last one to Richard Nixon based on conspiracy theories or right-wing memes.

On May 17, Trump posted online that, “word seems to be coming out that the Obama FBI ‘SPIED ON THE TRUMP CAMPAIGN WITH AN EMBEDDED INFORMANT.’” On May 20, Trump demanded, via Twitter, “that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration!” The following day, he quoted The Wall Street Journal, in asking, “‘WHERE IN THE WORLD WAS BARACK OBAMA?’”

For former Obama aides, it’s been a shock to the system—at times confusing in its complete removal from reality and, simultaneously, terrifying for the larger implications.

“To hear president of the United States even surmise that a previous administration was spying against him for political purposes, it suggests to me he doesn't appreciate those stringent controls that are in place,” said Ned Price, President Obama’s national-security spokesman. “This is either all pure show and theater and he knows as much or there is an idea in his head that this is possible and could have happened. What is really scary is that if he thinks it is possible that this happened, is he giving similar orders to his people?”