(CNN) President Donald Trump's aides are caught in a never ending game of catch-up, trying to translate his sudden, impulsive demands into instant policy.

They might deny it, but evidence suggests that a hurriedly announced deployment of National Guard troops to the southern border was sparked by a presidential tweet storm, itself apparently provoked by a Fox News story.

Just three days after Trump tweeted Sunday about reports showing a " caravan" of Central American m igrants trekking across Mexico, his administration is launching a mobilization of troops of undetermined length, rules of engagement and cost.

Homeland Security Secretary Kirstjen Nielsen insisted Wednesday that the plan had long been on the table -- and that it was a response to an expected increase in the number of people trying to sneak across the southwest border.

But its implementation days after Trump got an earful about his performance on immigration -- the animating issue of his 2016 campaign -- from conservative commentators at his Florida resort seems a huge coincidence.

So why today, rather than yesterday or tomorrow? Nielsen asked rhetorically. "Today is the day we want to start this process," she explained, without really explaining at all why the deployment had been so swiftly unveiled.

Questions about the reasons for the National Guard deployment only deepened Thursday, when Trump noted in a tweet that the caravan had largely been broken up by Mexico and highlighted historically low incursions across the US-Mexico frontier.

"Border crossings are at a still UNACCEPTABLE 46 year low. Stop drugs!"

The Caravan is largely broken up thanks to the strong immigration laws of Mexico and their willingness to use them so as not to cause a giant scene at our Border. Because of the Trump Administrations actions, Border crossings are at a still UNACCEPTABLE 46 year low. Stop drugs! — Donald J. Trump (@realDonaldTrump) April 5, 2018

A presidential roller coaster

Nielsen's explanation might have been more convincing were it not for a growing trend of out-of-the-blue policy edicts issued by an increasingly imperious President, who has apparently decided he's mastered the job and needs no restraints.

On March 1, Trump rocked his fellow Republicans and the rest of the world by announcing at a hurriedly arranged meeting with industry leaders that he would slap 25% tariffs on steel and aluminum imports.

His proclamation set off a frantic effort by officials to codify it into a workable policy, and then a subsequent panic while exemptions were worked out for some of America's closest allies.

Last week, Trump's shock and awe style caused another storm, when he announced as an aside at a rally in Ohio that US troops would soon be coming home from Syria.

As Washington tried to work out what he meant, one National Security Council spokesperson dispensed the classic quote always rolled out when a President tacks out well ahead of his administration on a policy issue.

"The President's comments speak for themselves," the official said.

The announcement, which surprised the Pentagon, came as another blow to European states that have troops in the fight -- and kicked off a rapid policy review that culminated in a new US holding position on Wednesday.

A senior administration official told CNN the President told his national security team that he will keep troops in Syria in the short term but made it known he wants them out soon -- leaving the long-term state of the mission in doubt.

CNN's Elise Labott and Kevin Liptak reported Wednesday night that the President grew irritated on Tuesday when his team told him that an immediate withdrawal from Syria, where US troops have been fighting ISIS, would be unwise and could not offer a timeline for when American soldiers could come home.

Diplomats said that both the tariff announcement and the Syria comments set off frenzies in allied capitals as governments rushed to decipher the President's sudden shifts and gamed out how they could mitigate damage.

Other recent examples of the new "unleashed" version of Trump bypassing a more pliant West Wing operation after a staff purge include his shocking snap decision to meet North Korean dictator Kim Jong Un -- a move that threw his top foreign policy advisers for a loop -- and his brusque firing of Veterans Affairs Secretary David Shulkin last week and announcement of his presidential physician, Ronny Jackson, as a replacement.

Trump is slipping constraints of conventional advisers

Trump supporters would argue that the President is merely showing decisive leadership and an increasing awareness of how to work the policy process to bounce the bureaucracy into enacting promises that he made to his supporters in the 2016 elections.

After all, though Trump's policy lurches came as a surprise in the moment, no one could be shocked that he wanted to strengthen the border, torch the global trading system or is skeptical of Middle East quagmires.

Yet Trump's gut-level leadership also reverses a traditional policy process that presidents of both parties have maintained, reasoning it can lead to good decisions and an awareness of the pitfalls of certain courses of action.

And given his propensity to stoke racial and cultural tensions at a time of political peril in order to preserve his support base and the vocal backing of conservative media, his sudden fixation with the border is bound to come under extra scrutiny.

Some of Trump's detractors argue that the President is short-circuiting a conventional policy process simply to indulge his whims and is making decisions involving national security to bolster his own political base.

Rep. Bennie Thompson of Mississippi, the top Democrat on the House Homeland Security Committee, argued Wednesday that the National Guard deployment was a case in point.

"I strongly question whether the Department of Homeland Security and the Department of Defense weighed in on this proposed use of our military or whether, more likely, they were caught completely off guard," he said.

Some worry that Trump's increasingly impulsive behavior could cause grave consequences in a fast-moving international crisis and reveals a governing system that fails to contain his impulses.

"I think that's a question of when, not if," one former senior official for a previous administration said, speaking on condition of anonymity, adding that it took any administration time to master the levers of power.

"If you have a sufficient number of enablers in place, there aren't a lot of checks on a President," the official added.

The haphazard nature of the National Guard deployment was revealed by the administration's different timelines on when troops would arrive.

Nielsen said she hoped the first deployments would take place "immediately" but a senior official later told reporters that "we expect personnel to be on the border quickly, but at this time we don't have a date."

Adding to the impression that the deployment order was rushed, after Trump's early morning tweet promising "strong action today," Nielsen was unable to give details of the size of the contingent, its specific mission or what it would cost to deploy and remain on station.

Yet later on, speaking to reporters on condition of anonymity, a senior official insisted that the decision hadn't been rushed, saying it had "been in discussion for a while per presidential direction."

Yet Lt. Col Tom Keegan, California National Guard spokesman, on behalf of the administration of Democratic Gov. Jerry Brown seemed to suggest that states were in the dark about the White House's intentions.

"We look forward to more detail, including funding, duration and end state," Keegan said.

Suspicions about the political motivation behind Trump's move are also likely to be stoked by the conditions on the ground near the border.