What plausible reason could Donald Trump have for trying so hard to discredit America’s intelligence agencies and their finding that Russia interfered in the presidential election? Maybe he just can’t stand anyone thinking he didn’t, or couldn’t, win the presidency on his own.

Regardless of his motives, the nation’s top intelligence officials were having none of his nonsense on Thursday. In an extraordinary pushback against the president-elect, James Clapper Jr., the director of national intelligence, told the Senate Armed Services Committee that he was “even more resolute” in believing that Russia not only hacked the computers of the Democratic National Committee and others but also disseminated classic propaganda, disinformation and fake news.

Flanked by the Pentagon’s top intelligence official and the head of the cyber command, Mr. Clapper acknowledged that the intelligence agencies can at times make mistakes. But he distinguished between presidential skepticism about their findings, which is healthy, and “disparagement” of the professionalism of the agencies, which is perilous for national security.

With his refusal to accept regular intelligence briefings on threats facing this country and his persistent denigration of the intelligence community, Mr. Trump has shown time and again that he worries more about his ego than anything else. He is effectively working to delegitimize institutions whose jobs involve reporting on risks, threats and facts that a president needs to keep the nation safe.