Who really gets under Donald Trump's skin? A man who has been dead since last year and another whom the president says he hardly knows.

At least that's the bizarre picture painted by Trump this week in angry rants at the late senator John McCain and a Washington lawyer called George Conway.

Trump lashed out yet again Wednesday at the broadly popular McCain, saying "I've never liked him much. I really probably never will."

This followed a series of tweets and other statements in the last few days raging at the former senator's politics, role in the Russia collusion probe, and personal intelligence.

As for Conway, "he's a whack job," Trump told journalists Wednesday. "A stone cold LOSER," he wrote on Twitter a few hours earlier.

The venom of the attacks was not unusual for a president who revels in put-downs. The targets of his ire, though, raised eyebrows.

McCain is widely remembered by Americans as a hero for his courage during six years of often brutal captivity in Hanoi during the Vietnam war.

More to the point, he died in August at 81. While he fell out over policy several times with his fellow Republican Trump, he's been buried for seven months.

No less curious is the Conway obsession.

A prominent lawyer in Washington circles but a nobody to ordinary Americans, Conway burst into the public eye because he is married to a senior White House aide and has begun loudly questioning Trump's mental stability on Twitter.

In both cases, Trump could have avoided controversy.

McCain, after all, can never clash with him again and Conway poses no real threat -- other than, perhaps, to the stability of his marriage to senior Trump advisor Kellyanne Conway.

Even Trump says, "I barely know him."

Backing off from a fight, however, wouldn't be Trump: his entire presidency is based on being combative. Or, as Kellyanne Conway, told Politico: "he's a counter-puncher." "His base sees this as classic Trump behavior," said Rich Hanley, who teaches on politics and the media at Quinnipiac University. "They expect Trump to swing at everybody, even ghosts."

Trump enjoys landing pithy, sometimes humorous, sometimes what many would call poor taste verbal blows. And Twitter, where he has more than 59 million followers, is his principal weapon.

The Twitter president has largely dispensed with formal news briefings, finding that a tweet alone can get everyone talking -- without giving them much chance for questioning.

Trump defended this method of communication on Wednesday as an antidote to what he calls the "corrupt" and "fake" media. By that, he means most standard news organisations.

"It's a way that I can get honesty out," he said.

It's a way where Trump typically gets to punch first and punch hard, thereby dominating the news agenda.

George Conway, however, has broken the mold.

Leveraging his position as husband to a Trump aide and posting outrage-seeking tweets that claim to diagnose personality disorders, he effectively out-trolled the troller in chief.

Trump's "not used to that. He's used to being the aggressor, the bully, the one who controls," Hanley said.

"Now he's finding that there are characters like Conway... who are more aggressive than he is and he doesn't know how to handle it." In a different sense, the same applies to McCain.

He's gone, but memory of the maverick senator, who was not afraid to break with Republican ranks or to hide his dislike for a president who ridiculed his capture in Vietnam yet never served himself, remains fresh.

Clearly much too fresh for Trump, who has talked so much this week about his disagreements with McCain that it sounds as if they had been locking horns only hours ago.

Trump just can't let go.

"My dad... would think it was so hilarious that our president was so jealous of him that he was dominating the news cycle in death," McCain's daughter Meghan said on ABC television Wednesday, demonstrating some put-down skills of her own.

With Trump soon starting his 2020 reelection campaign and Democrats launching their own nomination battle, the ugly back and forth is set to intensify.

But Mark Rom, a politics professor at Georgetown University, predicted that Democratic candidates will get surrogates to do the dirty work while they try to keep above it all.

Their mantra, he said, will be modelled on the icily dismissive approach taken by the House of Representatives speaker, Nancy Pelosi: "I'll just ignore that little man.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)