President Donald Trump on Friday again warned North Korea not to attack American interests or allies, as Mr. Trump tweeted out photos of U.S. military forces on the Pacific island of Guam, aiming his remarks directly at the leader of the Pyongyang regime, Kim Jong Un, again saying that any military action by North Korea will meet with a swift and serious U.S. response.

"If he does anything with respect to Guam or any place else that is an American territory or an American ally, he will truly regret it, and regret it fast," the President said in a Friday afternoon photo op at his golf retreat in New Jersey.

"I hope they are fully going to understand the gravity of what I said," Mr. Trump told reporters. "And what I said is what I mean."

Earlier in the day, Mr. Trump had sent out a clear message on Twitter as well to Kim and the Pyongyang regime.

"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely," the President tweeted.

"Hopefully Kim Jong Un will find another path," Mr. Trump added on Friday morning, a day after the President once more bluntly warned the North Koreans not to test U.S. military resolve, after threats by Kim to attack Guam.

"Let's see what he does with Guam," the President told reporters on Thursday, making clear that the U.S. would swiftly respond.

"If he does something in Guam, it will be an event the likes of which nobody has seen before -- what will happen in North Korea," Mr. Trump added.

As for the U.S. military, the Pentagon was quietly making it clear that if force is needed, then it will be available to take on North Korea.

On Capitol Hill, Democrats were raising red flags about a possible nuclear showdown with North Korea, with some asking House Speaker Paul Ryan to bring lawmakers back from their summer break, in order to debate issues of using nuclear weapons.

"It is critical that the Trump Administration exhaust all diplomatic options before resorting to military force," argued Rep. David Cicilline (D-RI).

"The president’s escalating rhetoric won’t calm tensions or facilitate diplomacy with North Korea," said Sen. Dianne Feinstein (D-CA). "He needs to step back from the brink."

As for Republicans, there was no evidence that they were deserting the President, or at all spooked over his tough talk against Pyongyang.

"It is entirely unacceptable to allow a nuclear intercontinental ballistic missile capable of reaching our western shores into the hands of Dictator Kim Jong Un," said Rep. Jack Bergman (R-MI).