WASHINGTON — It wasn't true, it wasn't true — until it was. Thursday's announcement that National Security Adviser H.R McMaster will be the latest top aide to leave the White House, replaced by John Bolton, spotlights President Trump's mercurial decision-making when it comes to staffing the top ranks of government.

Mr. Trump will discuss. Consider. Float. Leak. But nothing's decided until it's decided.

His personnel moves materialize in fits and starts — at once both glacial and impulsive. In the White House, they're called "long-term snap decisions." Bolton told Fox News Thursday night he didn't know the announcement would come that afternoon.

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McMaster showed up to work Thursday the same way he had for months: His days in the West Wing were numbered, but not even Trump knew how long he'd keep his aide around. Hours later, in a phone call between the two, it became clear that McMaster's time was up.

Mr. Trump had mused to advisers and outside allies about McMaster's ouster for months — the pair had never formed a strong rapport — and rumors of his replacement had swirled in Washington for months.

Just last week, it had appeared McMaster's departure was imminent — but White House officials insisted the speculation was false.

"Just spoke to @POTUS and Gen. H.R. McMaster — contrary to reports they have a good working relationship and there are no changes at the NSC," White House press secretary Sarah Huckabee Sanders tweeted a week ago.

Earlier this month, Mr. Trump called reports that McMaster was on his way out "fake news."

McMaster's departure was essentially reported to have been a fait accompli by last week by CBS News chief White House correspondent Major Garrett. Like ousted Secretary of State Rex Tillerson, McMaster had never really developed a strong relationship with the president.

Some White House staff rejected suggestions they had misled the public about McMaster's status. At the same time, they maintained the decision to remove him had been long in coming and was not a response to Tuesday's leak of briefing papers related to Trump's phone call with Russian President Vladimir Putin, a disclosure that had generated considerable criticism and fresh speculation that McMaster was in trouble.

They also insisted Sanders' tweeted assurances about McMaster were true — that even as Mr. Trump considered ousting McMaster, the president hadn't made the final call.

The timing of McMaster's departure in part had been complicated by efforts on the part of the president and Chief of Staff John Kelly to find a suitable landing pad for the three-star general, but one never materialized.

In the end, Mr. Trump went ahead with the personnel change nonetheless. Bolton, a foreign policy hawk, had been in conversations with Mr. Trump for weeks about taking the job, but had no indication he'd receive the offer Thursday until he was invited to the White House.

It was a familiar scenario after the firing last week of Secretary of State Rex Tillerson: His eventual departure had been viewed as a certainty ever since he was reported to have called the president a "moron" after a meeting on Afghanistan strategy last July. White House aides denied for months that a shakeup was afoot, even though Kelly had drawn up plans last fall to replace Tillerson with CIA Director Mike Pompeo.

It also fit the pattern set with other high-profile departures, including Trump's first chief of staff, Reince Priebus, and press secretary Sean Spicer. Each was long rumored to be leaving — but hung on and on until, suddenly, he was out.

As Mr. Trump takes a more active role in reshaping his White House, the same assertive decision-making style is beginning to surface on matters of policy. Trump grew frustrated by what he considered to be stalling on the part of the more moderate forces in his administration who opposed his calls for more protectionist trade policies. One day, with almost no warning, he cut them out of the loop and decided to pursue tough tariffs on global trading partners.

It's clear that the turmoil isn't subsiding.

Though the timing is, as ever, uncertain, Kelly is viewed to be one of the next to exit — and Cabinet secretaries like Housing Secretary Ben Carson and Veterans Affairs' David Shulkin are increasingly on thin ice. Current and former White House officials have maintained that once the president begins considering replacing one of his aides, the staffer is playing on borrowed time.

One White House official characterized the president's decision-making process in more literary terms, referencing Ernest Hemingway's quip on how one goes bankrupt: "Gradually, then suddenly."