When Donald Trump shows up for work next week, it's anyone's guess as to what he will do. Over the past month, many reporters have asked me "what do you think Trump will do and what are you most concerned about?". My simple answer has been "I know what worries me most, but I have no idea what he'll do because I don't think he knows either".

During the campaign, Trump promised a boatload of dramatic initiatives and actions. After winning, many have been substantially changed or just disappeared. Hillary Clinton isn't going to jail; Mexico isn't paying for a wall; Muslims aren't being banned; and, lest we forget, Wall Street and lobbyists aren't problems anymore (actually, they are now the government).

We'll soon see what Trump will do. If I had to guess, I'd assume that he'll undo some of President Obama's executive orders that protected air quality, water purity, consumers and workers. These will all, no doubt, be serious set-backs, but they won't make good on the new President's "big promises" to transform our country from the dark post-Apocalyptic nightmare of his speeches to his vaguely defined vision of being "Great Again". That will require more than "I promise you".

The job of being President is different than starring in a reality TV show, running a campaign, Tweeting, or being a real estate self-promoter. Boastful rhetoric and vainglorious promises may have defined Donald Trump's road to the White House but I fear that he may not be able to adjust to the challenges of being there. There are several reasons to be concerned.

Donald Trump likes to be in control, but as he will soon learn, the President is not so much captain of the team as he is captive of the team. He's not the only actor in this drama nor does he have complete control over events, or even over those who supposedly work for him. Being President is not as easy as starring in your own TV show or running a campaign. A President is dependent on staff for input and on their ability to execute. This might sound simple, but when you consider the degree to which Trump's cabinet appointees have already made clear in Senate hearings their disagreements with his views on critical issues and the extent to which the positions of some cabinet appointees differ dramatically from those of key White House staff (think of General Mattis versus General Flynn, or General Kelly versus Steve Bannon and Steve Miller), internal conflicts will make for messy decision-making.

The new President will also need Congress and the much maligned GOP establishment to support his agenda. And here too, his control will be limited. Republican leaders in both houses will give Trump a bit of a honeymoon, but they know that he starts his presidency with low approval ratings. With all Members of Congress and eight Republican Senators facing reelection in 2018, expect that Congress will soon start thinking more about their own careers and less about the success of the President's agenda. One big blunder, embarrassing incident, or ethics or financial scandal and we'll see how loyal Republicans will be to "their" President.

More significant than the difficulties the President will face in attempting to control competing staff or Congress will be his inability to control unforeseen events that will unfold at home or abroad. I often note that Presidents are judged less by their success in accomplishing the agenda they set for themselves and more by how they respond to the agenda set for them by an unpredictable world.

George W. Bush was confronted with the horror of 9/11, the devastation of Katrina, and the worst economic collapse since the Great Depression. He squandered the world's goodwill after 9/11, launching two disastrous wars and engaging in torture abroad and repression at home. He bungled Katrina and struggled to deal with the recession.

Barack Obama began his race for the White House before the recession hit. It was presented to him as an unwanted gift. He inherited an Israeli-Palestinian conflict reeling from the disastrous Gaza War and the election of an incorrigible and intransigent Israeli leader. He also had to contend with a resurgent Russia, an increasingly aggressive China, and the unsettling out-of-control consequences of the so-called Arab Spring. Obama successfully managed an economic turn-around while managing to pass a sweeping health care reform bill and other significant pieces of social legislation. But he had much less success in foreign affairs. Netanyahu was a persistent headache whom Obama felt pressured to deal with gingerly. His efforts to "reset" with Russia and the Muslim World failed, and his desire to "pivot to Asia" was stymied by domestic politics and the unraveling of the Middle East.

This inability to control people, institutions, and events will test the Trump presidency. He won't find it easy to fire whoever doesn't play by his rules. And unlike business, he won't be able to declare bankruptcy and get a "do over". In the White House, should he screw up--he, the rest of us, and possibly the entire world, will suffer the consequences (think of George W. Bush's Iraq war debacle).

As much as the new President has to be concerned about dissension within his Administration, an uncooperative Congress, independent-minded foreign leaders, foreign wars or terror attacks or other calamities that may occur, I am concerned with how a volatile and unpredictable Donald Trump will respond to situations he can't control. He hasn't demonstrated the patience, discipline, and thoughtfulness that will be required to handle complex issues and unexpected problems.

So yes, I am troubled by the prospect of Donald Trump undoing some of the key elements of Barack Obama's progressive agenda. But, to be honest, more than that I am concerned that on any given day, given what we've seen of his personality and what we know about the demands of the job he has now assumed, we could be one Tweet away from an international incident or one terror attack away from a campaign of mass repression.