Washington (CNN) Military brass are rethinking their plans for Syria. Trade experts have hurriedly drafted harsh new tariffs. Homeland Security officials are scrambling to bolster efforts on the border. And diplomats are scraping together plans for an once-unthinkable meeting with North Korea's despotic leader.

Spurring all those efforts: impulsive announcements by President Donald Trump , who has sent his administration racing to catch up. Political and career staffers alike have found themselves caught off-guard by announcements preceded by little deliberation or planning. In some cases, the rhetoric hasn't matched reality, forcing advisers to contort themselves to explain the President's moves.

"We'll let you know that as soon as we can," said Homeland Security Secretary Kirstjen Nielsen when pressed by reporters in the White House driveway for details of a new National Guard deployment to the US-Mexico border.

The particulars of the plan -- including whether the troops will be armed -- had yet to be formulated.

Asked when the number of troops sent to the border would be known, Nielsen said she was going to "get on phone calls right now" to help determine those figures.

Frenzied uncertainty

Inside the government agencies left to enact Trump's decisions, a sense of frenzied uncertainty has settled in, people familiar with the dynamic say. Top -evel staffers, hand selected by the White House, have little guidance on what decisions the President has made and is ready to announce. Even as senior West Wing aides work to erect a new structure around the policy implementation process, Trump has thrown wrench after wrench into their efforts.

Senior administration officials acknowledged this week that broad plans have long been on the table to dispatch US troops to the border to assist immigration agents. But they said those plans were far from ready to roll out when Trump announced his intentions on Tuesday.

The drastic new approach caught some of his top advisers off-guard, and there was little evidence afterward that a firm plan was in place before Trump made his decision public. Military leaders have largely been opposed to deploying troops to the border. Officials have been unable to detail the number of troops who will go, where they will serve or what precisely they will do.

Ultimately, it was Trump himself who had those answers Thursday when pressed by reporters aboard Air Force One.

"Anywhere from 2,000 to 4,000," was the range he offered for the number of deployed troops . He said they would remain until the border wall was complete. But he demurred when questioned about the costs.

"We're looking at it," he said. "I have a pretty good idea."

Trump's decision on the border -- along with his plans to withdraw from Syria, impose new trade penalties and meet with Kim Jong Un -- weren't necessarily surprising; he pledged to do all of that as a candidate. But despite those forewarnings, there is evidence the government apparatus is struggling to keep pace with a newly emboldened President.

Fulfilling campaign promises

Trump's aides describe him as both more comfortable in his role and newly eager to fulfill his campaign promises as critical midterm elections approach. He has shed some senior advisers who advised against impulsive decisions, and has resumed speaking with aides who encourage his gut instincts.

During dinners at the White House and in conversations at his Mar-a-Lago club, Trump has been encouraged to return to his campaign persona, people familiar with the conversations say. He has been warned that support among his conservative base of voters could soften if he doesn't begin fulfilling his campaign vows at a rapid pace.

The issue of a "caravan" of Central Americans moving toward the United States had been covered heavily by Fox News amid his outburst, and he spoke with several Fox News personalities during his Easter weekend in Florida.

In past administrations, decisions that involve troop deployments have been weighed extensively by the President and top military officials before being publicly announced. But on Tuesday, after Trump made his declaration about the border, the White House struggled to explain what he meant. Later in the day, it was announced that Trump had met with his Defense Secretary James Mattis and other top administration officials to discuss immigration strategy.

It was the second time in a week that Pentagon officials found themselves surprised at an unexpected public declaration from the President. Speaking in Ohio, Trump told a crowd of union workers that US troops would "be coming out of Syria, like, very soon," a declaration that few inside the Pentagon expected was coming.

While Trump has privately been telling advisers since February he wanted to make an early exit from Syria, he's been warned that a withdrawal now could erode gains made against ISIS. During a testy national security meeting on Tuesday , Trump grew irritated when those warnings were aired again. He told his team that they would ideally develop plans to defeat ISIS and pull US troops out of the country within six months.

It's a steep demand for a national security team already scrambling to prepare for talks with North Korea's Kim, which Trump agreed to on the spot when a South Korean delegation came bearing an invitation from the North. Few of Trump's advisers were anticipating the move.

"This is not careful, modulated foreign policy where we're thinking three or four moves ahead," said Richard Haass, the president of the Council on Foreign Relations who served Republican and Democratic presidents. "This is foreign policy one impulse, one tweet, one step at a time. We're playing against people who think much more strategically."

Kelly's role

There was a time in the Trump administration when chief of staff John Kelly was regarded as a savior of functional policy process after a series of missteps and rushed announcements. His efforts to shepherd through massive tax reform legislation were well-regarded by the President and congressional Republicans.

But even those efforts have been subject to Trump's whims. At an event in West Virginia on Thursday arranged to herald the tax measure, Trump made a dramatic show of tossing his page-long prepared speech into the air. He chose instead to discuss, in harsh terms, the immigration matter.

"To hell with it," Trump said as the discarded speech fluttered to the ground. "That would have been a little boring."

Kelly's strict management style has clashed with the President's freewheeling instincts, Kelly's stature has been reduced. Trump no longer consults with him on every policy announcement, and Kelly has found himself as caught off guard by certain announcements as other aides, White House officials say.

That included Trump's impromptu announcement during a meeting last month that he was imposing new tariffs on steel and aluminum -- a vow he'd long promised but that few aides, including Kelly, knew was coming. In the following week, staffers hastily drafted the language, which required extensive legal vetting. Up until the morning Trump signed the orders, it was unclear whether the documents would be ready for his signature.

Still, Kelly has continued working to impose more order on the policy process, even as he finds his influence slipping. He installed a new deputy for policy coordination, Chris Liddell, who told staffers during a meeting last week that new structures would be enacted for policy rollouts and implementation, according to a White House official.

But since then, Trump has announced by himself new policy initiatives for Syria and the border, with little sign of pre-planning.

"It appears to be government by impulse rather than government by deliberation," said David Gergen, a CNN political analyst and co-director of the Center for Public Leadership at Harvard Kennedy School who served as an adviser to four presidents. "And that does cause waves of anxiety and scrambling among people around him."