Washington (CNN) Nearly five months ago, President Donald Trump bid farewell to a grinning Barack Obama , waving as the military helicopter shuttling his predecessor into post-White House life got smaller and smaller.

They haven't spoken or seen each other since.

For a President who seeks extensive counsel from outside the White House -- in calls to old friends, business executives, and even despotic foreign leaders -- Trump has largely forgone advice or guidance from any of the men who have held his job previously.

In the months after Trump and Obama carried out a peaceful hand off of power, the two have failed to develop any sort of working relationship, according to White House advisers and former administration officials.

They have not spoken over the phone, at least to the knowledge of their aides. Neither has made any real attempt to reconcile after Trump accused Obama of ordering wiretaps at his skyscraper in New York.

Perhaps it's a predictable outcome for two men with a long and bitter history; to be sure, the ice-out is the product of deep-rooted enmity that extends well beyond differences in policy or style.

But in the scope of recent history, it's unprecedented for a sitting president and his predecessor to eschew even the faintest of ties.

"I don't think they have a relationship," said David Axelrod, who served as Obama's senior adviser during his first years in office. "President Obama did what he could to help during the transition but, obviously, there have been intervening events."

Not always frosty

It wasn't always so frosty. In the days following Trump's victory in November, Obama made a concerted effort to help guide his successor into place, despite personal animosity extending back to Trump's birther conspiracy. They spoke for more than an hour in the Oval Office, and Trump declared they'd developed "warm" ties.

Cracks emerged before long, with Trump intervening in a dispute over Israeli settlements and later lashing out at the sitting President on Twitter. But on Inauguration Day, all appeared cheery as Obama and his wife welcomed the incoming first family to the White House for coffee.

Once Trump was installed in office, however, things progressively soured, culminating in Trump's March tweets accusing Obama of ordering surveillance of Trump Tower.

The baseless claim, which Obama's team denied, was said to irk and exasperate the former President. There was an effort to smooth things over, including in conversations between Trump's White House chief of staff, Reince Priebus, and Obama's former White House chief of staff, Denis McDonough.

But the talks never produced a phone call between the current and former presidents. And Trump, who hasn't backed down from his claim, continued his attacks on his predecessor.

"Well, he was very nice to me, but after that we've had some difficulties," Trump told CBS News in an interview in early May. "He was very nice to me with words and when I was with him. But after that there has been no relationship."

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Obama reemerges

Since he made those comments, Trump has warily eyed Obama as he reemerges into public life. The two men were both in Europe last month, Obama for an appearance with German Chancellor Angela Merkel in Berlin and Trump for summit meetings with his new foreign counterparts.

Trump's first talks at NATO headquarters in Brussels had to be shifted to the afternoon to accommodate Merkel's schedule with Obama, according to people familiar with the meeting's planning.

This week, Obama met with Canadian Prime Minister Justin Trudeau after delivering remarks in Montreal that warned against authoritarianism -- remarks that were seen as veiled jabs at Trump.

Both Merkel and Trudeau participated in sometimes-tense G-7 meetings last month in Sicily, where Trump was isolated on issues like climate change.

Republicans close to Trump say Obama's active schedule with foreign leaders has caught the President's eye as he works to develop his own relationships with world leaders. But they stopped short of saying Trump has expressed worry about Obama's private conversations with foreign leaders.

"Even though President Trump may not like it, having Obama out there speaking with leaders, even if it's critical of Trump, is probably helpful," said Julian Zelizer, a presidential historian at Princeton. "He might be serving a diplomatic role that the administration itself is not fulfilling."

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Presidents Club

Presidents have long relied on their predecessors for advice on a job few could possibly understand. Sometimes they have called on members of the so-called Presidents Club to carry out tasks on behalf of the United States.

The current shutdown in ties between Trump and Obama amounts to the first time in decades a sitting president has closed off all communication with his predecessor -- and, by extension, one of the only individuals with direct knowledge of a role few have played.

"There are only six people on the planet who fully understand the demands of that job," Axelrod said. "It's often helpful, but certainly not mandatory, to be able to counsel with them. But that's totally up the discretion of the incumbent, who in this case has without evidence accused his predecessor of what would amount to a crime. That suggests to me that they're probably not chatting much."

In early June 2001, George W. Bush encountered his predecessor Bill Clinton at a Boston funeral in their first in-person meeting since the handoff of power months earlier. The two men sat in the same pew of St. Brigid's Church alongside Al Gore -- Clinton's vice president who Bush ultimately defeated after a prolonged court battle the prior year.

As Bush's presidency wore on, he and Clinton developed friendly ties, speaking by phone with some regularity about the aspects of the job only they could understand.

Days before taking office, Obama convened all the living presidents to solicit advice about the job. Bush hosted the session in his private dining room. Historians said it was the first time all living presidents had convened at the White House.

About a month later, Obama placed an unusual phone call to his predecessor to inform Bush he was planning to announce a withdrawal of troops from Iraq -- a conversation Obama's aides said was a "courtesy" to the man who began the war that Obama ran vowing to end.

The phone call, made from a holding room at Camp Lejeune in North Carolina, was brief, but it did reflect open lines of communication between political and ideological opposites -- a channel that thus far hasn't been dug between Obama and Trump.

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Open hostility

Last week, when Trump decided to withdraw the United States from the Paris climate accord, few even questioned whether Obama -- whose administration helped broker the landmark agreement -- would be given a heads up. Instead, Trump tore into Obama for negotiating, in his view, a humiliating deal that had foreign leaders laughing at the US.

Obama, in one of his first overly political statements since leaving office, declared Trump's decision to "reject the future" deeply misguided.

Withdrawing from the Paris agreement was one of the most consequential announcements of Trump's young presidency, which has been most successful in reversing Obama policies.

In taking those steps, Trump has made little effort to mask his disdain for his predecessor or his decisions, the open hostility reflecting a harsher tone than presidents past who took the country in new directions.

Even bitter rivals have found ways to reconcile.

Despite griping in private about each other's shortcomings, John F. Kennedy and Dwight D. Eisenhower carried out regular consultations about national security matters after Kennedy took power from the Army general in 1960.

Only three months after taking office, Kennedy was strolling the grounds of Camp David with Eisenhower discussing the botched Bay of Pigs invasion.

"No one knows how tough this job is until after he has been in it a few months," a bewildered Kennedy confessed to Eisenhower, according to his biographer Stephen E. Ambrose.

"If you will forgive me," Eisenhower replied, "I think I mentioned that to you three months ago."