Bridgewater, New Jersey (CNN) In 1962, as the United States and the Soviet Union wobbled toward nuclear confrontation, then-President John F. Kennedy got his predecessor on the phone.

"What's your judgment as to the chances they'll fire these things off?" Kennedy asked Dwight Eisenhower, a retired Army general whom he'd once derided as a "cold bastard."

Consultation between two presidents during moments of crisis was once routine. When Harry Truman faced calamity in Europe, he secretly asked Herbert Hoover, one of his predecessors, for help. When Barack Obama faced a humanitarian crisis after an earthquake rocked Haiti, he called on Presidents Bill Clinton and George W. Bush to step in.

Now, as North Korea presents fresh nuclear danger, those types of consultations appear to be history.

President Donald Trump, six months into his presidency and facing simmering tensions in Asia, has not only ignored his predecessors, he's rekindled his deep-seeded animosity for the man who handed him the nuclear codes.

This week, as Pyongyang issued threats to launch missiles at Guam, Trump retweeted a series of messages that criticized Obama, including an unscientific Twitter poll that had been inactive for days.

Who is a better President of the United States? #ObamaDay — ProgressPolls (@ProgressPolls) August 4, 2017

"Who is a better President of the United States," the poll asked, using the hashtag #ObamaDay to note that the state of Illinois will now mark August 4, the former president's birthday, as Barack Obama Day.

"@POTUS being unpredictable is a big asset, North Korea knew exactly what President Obama was going to do."- @jessebwatters — The Five (@TheFive) August 10, 2017

Trump also retweeted two messages on Wednesday evening, one from a Fox News show and another from John Bolton, a former ambassador to the United Nations, that knocked Obama.

Our country & civilians are vulnerable today because @BarackObama did not believe in national missile defense. Let's never forget that. — John Bolton (@AmbJohnBolton) August 9, 2017

Obama has long been a foil for Trump , who seems to rotate through perceived enemies every few weeks. Earlier this summer it was Hillary Clinton, the former secretary of state he defeated in last year's election. Before that it was his own Attorney General Jeff Sessions, an ardent supporter whom he nonetheless declared "weak" and "beleaguered."

Their spat is conducted from afar; Trump has not spoken with Obama since the pair parted ways on January 20. Before that, their face-to-face conversations were limited to a meeting in the Oval Office and pleasantries over coffee ahead of Trump's swearing-in.

Trump's tussles this week with an increasingly hostile North Korea only serve as a reminder of those brief conversations with Obama. In the Oval Office the week he won, Obama warned North Korea would present Trump with his gravest global challenge. Trump later suggested he and Obama discussed the matter further during a shared limousine ride from the White House to the US Capitol on Inauguration Day.

It was the last time they spoke.

"This President has a very unusual obsession with his predecessor and constantly comparing himself to President Obama," Derek Chollet, former assistant defense secretary under Obama. "This is not a president who seems to be singularly focused on what is a genuinely a global security threat in North Korea."

"I think he has got to be shaking his head," Chollet said of the former president. "Clearly, he tried in raising this issue with President Trump by singling it out in their meeting in the Oval Office last year."

Speaking from his golf club here on Thursday, Trump maligned Obama's stance on North Korea, suggesting Obama had ignored an issue that he is intent on confronting.

"You look what happened with Obama. Obama -- he didn't even want to talk about it. But I talk," Trump said on the steps of his clubhouse. "It's about time. Somebody has to do it. Somebody has to do it."

Much of Trump's initial governing agenda has focused on reversing Obama's legacy, either on climate change or trade or diplomatic relations with Cuba.

Trump has grown frustrated in areas he hasn't been able to separate himself from his predecessor, according to a senior administration official. He's lashed out at his national security council for presenting strategies in Afghanistan and against ISIS that aren't markedly different from the previous administration's. When his team insisted he re-certify Iran's compliance with the multi-nation nuclear deal, Trump balked and took the disagreement public.

JUST WATCHED Trump tries to shift hacking focus to Obama Replay More Videos ... MUST WATCH Trump tries to shift hacking focus to Obama 04:48

Obama, it seems, is never far from Trump's mind, at least based on his public comments and his statements on Twitter.

"I inherited a mess," Trump said in February during the only solo press conference of his presidency. "It's a mess. At home and abroad, a mess."

Abroad, too, Trump has slammed Obama.

Standing next to Polish President Andrzej Duda, Trump blamed Obama for Russia's meddling in the 2016 election, saying that he did nothing to counter their attempt to help Trump and damage Clinton.

"Barack Obama, when he was president, found out about this, in terms of whether it was Russia, found out about it in August," Trump said. "Now the election was in November. That's a lot of time. He did nothing about it."

Trump's disdain for Obama, according to those close to him, was cemented when the then-President took aim at the reality TV star during the 2011 White House Correspondents' Dinner, mocking Trump as a conspiracy theorist whose most consequential decisions are whether to fire people on his TV show.

Omarosa Manigault, a former contestant on NBC's "The Apprentice," Trump's reality show, told PBS in 2016 that she thought at that time that Obama was "starting something that I don't know if he'll be able to finish" by publicly slamming Trump during that event.

Manigault, now a White House aide, said "every critic, every detractor, will have to bow down to President Trump" when he wins.

"It's everyone who's ever doubted Donald, who ever disagreed, who ever challenged him," she said. "It is the ultimate revenge to become the most powerful man in the universe."