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He also has a tendency to announce one thing and then reverse himself within days, or hours.

For better and for worse, Mr. Trump is a chronic waffler. As such, the American public would do well to stay vigilant about what his administration is up to — and not be shy about applying pressure.

It has long been clear that Mr. Trump is not the decisive, resolute leader he imagines himself to be. His presidency is littered with plans and pronouncements that were walked back or abandoned — some good, some not so good. His announcement last December that he was pulling all American troops from Syria was dramatically revised after pushback from foreign allies, lawmakers and his military advisers. This June, he approved military strikes on Iran in retaliation for its downing of an American drone, then canceled them. Last month, facing market turmoil and concerns from retailers and business groups, Mr. Trump postponed imposing additional tariffs on some Chinese consumer goods until after the start of the Christmas shopping season. He also floated the idea of cutting payroll taxes to goose the economy, only to reverse himself a day later with a declaration that the economy was plenty “strong.” Responding to back-to-back gun massacres, the president vowed to push for “sensible, important background checks” — until the National Rifle Association voiced its displeasure. At that point, Mr. Trump’s resolve wilted faster than you could say “$30 million in campaign contributions.” Not that he would admit to folding. He instead spent weeks offering rambling comments about possible legislation. The White House is expected to clarify his latest position soon.

Even with issues central to Mr. Trump’s brand, he will now and again give ground. Recall last summer’s policy of separating migrant children from their parents — a move so appalling that even some of the president’s Republican apologists could not stomach it. After six weeks of international uproar, Mr. Trump announced an end to the practice.

He executed a similar flip-flop this winter, when Congress’s refusal to give him billions in border wall funding led him to provoke a partial government shutdown. When the public grew grumpy enough about the disruption, the president caved and signed a bill that did not include his desired wall money.