Rep. Adam Schiff, the highest-ranking Democrat on the House Intelligence Committee, said that “the most alarming national security development” in the last week was Donald Trump alleging on Twitter, without any evidence, that millions of illegal immigrants had voted and cost him the popular vote.

“It demonstrates that the president is not undertaking the most important part of the transition… that is, growing into the job, recognizing the seriousness of the job,” Schiff told reporters at the Christian Science Monitor breakfast Tuesday.

The second reason, Schiff continued, was that it undercut the incoming president's credibility among the American public, as well as foreign enemies and allies. The California Democrat used the example of the Sony hack, when the Obama administration fingered North Korea as the nation state behind the intrusion, but declined to provide the exact methods that the intelligence community used to determine this—“that only works when the president has credibility,” Schiff said.

Trump’s sharing of falsehoods has implications, Schiff said, for whether Pakistan is to take seriously Trump’s offer to visit the country; or for whether China is to take offense at his outreach to Taiwan.

“When you have a president-elect who sends out patently false information, like the allegation that millions of undocumented immigrants voted, that impugns the credibility of the president, and at some point the president is going to need to be believed by the country,” Schiff said. “That’s going to have some serious consequences because our friends and our adversaries may not know whether the president means what he says.”

—Tim Mak