For wary Washington journalists, it seemed only a matter of time before Donald J. Trump’s presidency would lead to a high-tension standoff between his administration and the news media.

But on Day 1?

The news media world found itself in a state of shock on Sunday, a day after Mr. Trump declared himself in “a running war with the media” and the president’s press secretary, Sean Spicer, used his first appearance on the White House podium to deliver a fiery jeremiad against the press.

Worse, many journalists said, were the falsehoods that sprang from the lips of both Mr. Trump and Mr. Spicer on Saturday. Mr. Trump accused the news media of confecting a battle between himself and the intelligence services (in fact, he had previously compared the services to Nazi Germany in a Twitter post). And among other easily debunked assertions, Mr. Spicer falsely claimed that Mr. Trump’s inauguration was the most attended in history (photographs indicated it was not).