 -- President Donald Trump's two adult sons are defending their father's controversial Twitter attack against London Mayor Sadiq Khan.

In an exclusive interview with ABC News Chief National Correspondent Tom Llamas, Donald Trump Jr. and Eric Trump argued that London isn't doing enough to root out terrorism in the wake of Saturday's deadly attack.

“We keep appeasing it,” Donald Trump Jr. said Monday in Trump Tower. “And we keep saying, "Okay, it's gonna be great. We're gonna hold fast and we're gonna ‘keep calm and carry on.’ Maybe we have to keep calm and actually do something.”

The phrase “Keep Calm and Carry On” comes from a motivational poster displayed in Great Britain during World War II, and has since been revived as a symbol of the country’s “stiff upper lip” mentality when confronting adversity.

President Trump has drawn harsh criticism for attacking Khan in the aftermath of Saturday’s attack. In a series of tweets, Trump misconstrued a statement by the mayor saying there was “no reason to be alarmed” over increased police presence in the city.

Not mentioned by Trump was that Khan also warned that the threat level in London remains severe.

“Severe means an attack across the country is still highly likely, and so we have all got to be vigilant,” Khan said.

“You should be alarmed,” Eric Trump told ABC News. “Because this has become the new norm. And it's not right. And we, as a society, especially as Americans, better do something about it.”

When asked to respond to President Trump’s tweets, Khan said Tuesday he had “no time” to do so as he dealt with the attacks that killed seven people and injured 48 others.

“We aren’t going to allow anybody, whether it’s Donald Trump or anybody else, to divide our communities,” Khan said.

But Donald Trump Jr. argued Khan had also engaged the president -- potentially a reference to Khan’s past criticism of Trump’s proposed U.S. travel ban on people from six Muslim majority countries.

“Maybe rather than the mayor of London attacking, maybe he should do something about it,” Trump Jr. said. “Maybe he should do something to fix the problem rather than just sit there and pretend there isn't one.”