Most Americans who pay attention to politics have figured it out by now: Donald Trump doesn't back down from a fight, especially when it's a war of words fought over the television airwaves.

Now, one of America's closest allies is learning just how loud the Republican presidential front-runner's bark can be, too. Making an appearance on British morning show "Good Morning Britain," Trump sat down with Piers Morgan, the onetime CNN host. And Morgan essentially asked, why the beef with all of these British politicians?

First it was members of the British Parliament, some of whom wanted Trump banned from the country under rules that allow customs and immigration officials to turn away potential visitors who spread hate speech. Then, Prime Minister David Cameron joined in, calling Trump's plan to ban Muslims from entering the United States "divisive, stupid and wrong."

"I think if he came to visit our country, he'd unite us all against him," Cameron said.

And just last week, London's first Muslim mayor-elect, Sadiq Khan, had his say. (Trump has previously said Khan is one of a select few Muslims who would be exempted from his proposed ban.)

"It's not just about me. I don't want to be the exception, to be allowed to go to America," Khan told the BBC last Tuesday. "My concern is he's playing into the hands of extremists who say it's not compatible to be Western and to be mainstream Muslim."

Asked whom he'd support in November's general election, Khan was unequivocal.

"You won't be surprised to know that I will be backing the Democratic candidate, Hillary Clinton, who I suspect that it will be," Khan said. "And I hope she trounces him."

So when Morgan asked for his reaction to the criticism from Cameron, Parliament and Khan, he got an unsurprising response.

"Now, I don't care about him," Trump said. He later added, referring to Cameron's comments about his proposed ban on Muslims, "Number one, I'm not stupid, I can tell you that right now. Number two, I'm a unifier. Unlike our president now, I'm a unifier."

Judging from their recent comments, British politicians are still waiting to see evidence of No. 2.