In times of crisis, credibility is an American president’s most valuable currency. It’s one thing for a foreign partner to doubt a president’s judgment; it’s entirely more debilitating when that partner doubts the president’s word.

As President Trump confronts the twin challenges of North Korea and Syria, he must overcome a credibility gap of his own making. His insistence on remaining the most prominent consumer and purveyor of fake news and conspiracy theories is not only corrosive of our democracy — it’s dangerous to our national security. Every fact-averse tweet devalues his credibility at home and around the world. This matters more than ever when misinformation is a weapon of choice for our most dangerous adversaries.

Part of the problem is that Mr. Trump’s itchy Twitter finger can’t resist bluster. A series of sophomoric presidential missives — “North Korea is behaving very badly”; “North Korea is looking for trouble”; if China won’t help, “we will solve the problem without them! U.S.A.”; North Korea’s quest for a nuclear-tipped ICBM “won’t happen!” — has given Pyongyang a rare chance to take the high road. “Trump is always making provocations with his aggressive words,” its vice foreign minister declared.

Presidential bravado also risks North Korea taking him at his word, and miscalculating accordingly. Loose threats of pre-emptive military attacks could cause its leader, Kim Jong-un, to shoot first and worry about the consequences later — perhaps striking South Korea with conventional weapons to remind the world what he is capable of, if the United States seeks to eliminate his nuclear program. That’s a quick path to conflict with a volatile and nuclear-armed adversary.