President Trump’s shifting positions and outright lies have presented the American public with dueling narratives at every turn.

“He says so much, you can’t really pin him down,” said Julian E. Zelizer, a Princeton history professor and editor of a book of essays about Mr. Trump’s first term. “The point isn’t to have a contradiction, the point is to have cover.”

Tony Schwartz, the ghostwriter of Mr. Trump’s book “The Art of the Deal,” has said the president has one goal. “His aim is never accuracy,” Mr. Schwartz wrote in an opinion essay during Mr. Trump’s first term, “it’s domination.”

Experts say the dissonance can become dangerous. “Once you undermine consistency, the shared sense of reality, you’re undermining the basis of democracy,” said Jason Stanley, a Yale professor who has written books about propaganda and the erasure of history. “If there’s no shared sense of reality, we can’t collectively make decisions. So the only decision maker will be the disrupter in chief.”

Mr. Stanley said Mr. Trump’s contradictions boil down to a simple truth.

“If you’re constantly contradicting yourself,” he said, “you’re constantly lying.”