Donald Trump and Barack Obama haven't spoken since Inauguration Day as the relationship between the two men continues to crumble, according to two media reports.
Obama was described as irked and exasperated after Trump's claim that he was responsible for wiretaps during the presidential campaign, CNN is reporting.
The news network said Obama and his aides were left in disbelief after Trump made his charges on Twitter.
Both CNN and The Wall Street Journal say the two men have not been in touch since Jan. 20 when Trump was sworn in.
The budding feud between the two goes against a tradition of an "almost unwritten rule that you treat your predecessor with a degree of grace and decorum," said Douglas Brinkley, a presidential historian.
"There are these kinds of things that have happened in the past, but nothing to the degree where a sitting president would charge his predecessor with a felony," Brinkley said. "It creates a feeling of instability in the United States."
Trump is convinced Obama loyalists, who are still in government positions, are responsible for damaging leaks and believes the former president tapped his phones during the campaign, the Journal noted.
And the newspaper used stronger terms than CNN in describing Obama's demeanor after Trump's wiretap accusations. It said Obama was "livid" over the claims.
While the two have not talked, Trump had attempted to call Obama to thank him for a letter he had left for him in the Oval Office. Obama, who was traveling at the time, never responded, the newspaper said.
Historians note other presidents have endured stormy relationships with those who came before them, according to The New York Times.
"Trump is on new ground in going after Obama," said historian Robert Dallek.
Most presidents have publicly ignored their predecessors "until we get to Trump," he added. "He is either ignorant of recent presidential history or simply doesn't care."
But former House Speaker Newt Gingrich summed up Trump's feeling this way:
"It's a sign of how deeply frustrated he is. They have a much bigger assault against them than people have had in the past."