His latest shots at the late John McCain and his escalating social media altercation with George Conway , the husband of White House counselor Kellyanne Conway, are the latest examples of how the President just cannot resist a fight. But they also offer a fresh glimpse into a personality that is built on conflict, the search for an enemy and an insatiable quest for personal victories.

Sometimes the President initiates a clash. At other times he revives old battles like a warrior consumed by previous victories.

Even though McCain died nearly seven months ago, Trump cannot put their acrimony -- which caused the late Arizona senator to plan his funeral as an extended rebuke to the President, to rest.

He explained to reporters in the Oval Office Tuesday why he is still taking shots at the Vietnam war hero, including in a recent Twitter rant.

"I was never a fan of John McCain and I never will be," Trump said, citing his foe's vote against a GOP effort to repeal Obamacare.

"I think that's disgraceful, plus there are other things," he said.

For his critics, Trump's obsessions with McCain and other foes are not just unseemly. They are a sign of a man who is poorly suited to the job of President, and even temperamentally unfit to serve as commander in chief in a dangerous world.

But Trump's refusal to let bygones be bygones is also a political device. He's used the endless personal battles to stir up his base and give them something to unite against. The feuds offer definition to his life, his business, his 2016 campaign -- where he picked off a golden generation of GOP candidates one by one -- and now his presidency.

The President reopened hostilities with George Conway on Tuesday morning, after the well-known lawyer on Monday tweeted a definition of narcissistic personality disorder to suggest that Trump showed many of the symptoms.

"A total loser!" Trump wrote, while retweeting a claim by his 2020 campaign manager Brad Parscale that Conway was sore because Trump refused to give him an administration job he wanted.

Conway was quick to double down in their feud, tweeting at the President: "Congratulations! You just guaranteed that millions of more people are going to learn about narcissistic personality disorder and malignant narcissism! Great job!"

Kellyanne Conway said Monday she did not share her husband's "concerns" about Trump's mental state.

Old feuds burn bright

Trump's propensity to wage old feuds was evident in his wild tweet storms this weekend. He again went after John McCain -- even though the Republican senator from Arizona has been dead for nearly seven months.

The President mocked the Vietnam War hero, inaccurately for coming in "last in his class," and rebuked him for voting against a GOP bid to repeal Obamacare.

Trump can rarely leave "Crooked" Hillary Clinton alone either -- apparently not content with beating her in the 2016 election.

He rarely gets through a week without taking a shot at former President Barack Obama -- and often seems largely motivated by undoing his predecessor's legacy -- perhaps in revenge for being mocked at the White House Correspondent's Dinner in 2011.

And he's still simmering over past showdowns with other nemeses, such as the NFL : Some of the league's aficionados have traced Trump's fury over players taking a knee and team owners' reactions to his anger at failing to secure a franchise in the league in the 1980s.

"The $40,000,000 Commissioner must now make a stand," Trump demanded in a tweet at the start of last season.

Former Attorney General Jeff Sessions was never allowed to forget the President's fury at Sessions' recusing himself from the Russia investigation -- and Trump's anger is prone to pop up from time to time even though the former Alabama senator left office last year.

The President, for instance, blasted Sessions as "another beauty" in a tweet storm against senior Justice Department officials in February.

For a time, Trump was involved in an ugly personal spat with NBA superstar LeBron James -- insinuating in a tweet last year that King James wasn't very smart -- one of many of the President's altercations that have seemed to have racial overtones.

The President fed another ancient grudge over the weekend -- taking a new shot at NBC's "Saturday Night Live," which has caught his ire repeatedly because of Alec Baldwin's searing impression of him.

And he never lets up on his duel with reporters, who he has called "enemies of the people."

Trump has his foreign targets too, and returns to them again and again. He harbors a particular grudge for German Chancellor Angela Merkel -- but any US ally that he sees as freeloading off American generosity is especially likely to get a tongue lashing.

Never let it go

For Trump's critics, his refusal to let a fight go -- even ones that he has won -- speaks of a brittle personality that is not just off-putting but is dangerous in a commander in chief. Trump's tweet storms over the last three days, in which he blasted GM , the "fake news" media, McCain, insufficiently supportive Fox News anchors, Joe Biden and other targets came as much of the world was consumed by a true outrage: the aftermath of attacks on mosques in New Zealand , which killed 50 people.

Though Trump condemned the attacks on Friday, he shrugged off questions about a worrying rise in white supremacist groups and did not offer direct empathy to Muslims -- raising new questions about his history of anti-Muslim rhetoric.

Yet the President's boiling feuds are just one area in which opinion about him is irrevocably polarized.

The Trump base has never had much time for McCain -- even if taking potshots at a dead war hero might appear unseemly.

The "lock her up chants" that ring through Trump rallies express his supporters' views of Clinton.

In fact, the endless battles that Trump wages, while rendering him unfit for office in the eyes of critics, are exactly the kind of politically incorrect behavior that made him so popular with his supporters in the first place.

Those Americans don't believe Trump is on a mental precipice or that his frenzied, self-obsessed tweeting makes him unfit for the presidency.

A lesson of the last three years in politics is that the outrage of the media and elite opinion in cosmopolitan cities doesn't just fail to weaken the President, it often strengthens him -- one reason why he picks the fights he does.

Not every audience interprets Trump's flights of outrage the same way.

After an expansive attempt to discredit special counsel Robert Mueller, facilitated by conservative media, Trump may insulate himself to some extent from the outcome of the Russia investigation.

His weekend assaults on management and the unions linked to the closure of a GM auto plant in Ohio could be seen as gross presidential interference in the affairs of a private company. But the fact that the President is so fixated on the issue on a Sunday afternoon could be interpreted by others as evidence that he cares about honoring a campaign promise to reinvigorate US manufacturing.

"In many cases -- I am not saying in every case -- he is saying a lot of the same things that people are talking about around their neighborhoods, around their dining tables, at their watering holes," said Marc Lotter, strategic communications director for Trump's 2020 campaign, on CNN.

"And that is why he is connecting with people," he said.

Approval rating

Trump's all-fighting-all-the-time presidency certainly works with those Americans who like him best. Though the cycle of constant conflict is one reason why his re-election is far from assured even with the economy cruising and with unemployment as low as it's been in 50 years.

Conservatives are likely to be far less concerned than Trump's opponents about his condemnation of the attacks in New Zealand, which he called a "horrible massacre" on "sacred places of worship" while not condemning the white supremacist extremism that seems to have been their trigger.

It doesn't look like not reaching out to Muslims after the attack is going to hurt him with the base much either.

For much of the weekend, however, it seemed as though Trump had walked into a trap in the Oval Office on Friday when he told reporters that he didn't think white supremacist movements were a growing problem around the world.

His comment unleashed a global torrent of criticism and critical media coverage.

But if Trump's intention was to ensure he did not get too far out ahead of his base he may have been the one springing the trap -- positioning himself yet on one side of a confrontation with the media likely to solidify his base.

"The Fake News Media is working overtime to blame me for the horrible attack in New Zealand. They will have to work very hard to prove that one. So Ridiculous!" Trump tweeted on Monday.

Yet Trump's strategy -- constantly feeding his base's more inflammatory political instincts to solidify his position -- comes with risks.

A more popular rival than his old sparring partner, Clinton, and a more energetic Democratic base could make his path to re-election even more narrow.

If so, governing by feud may turn out to have been a big mistake.