Ever since Franklin Roosevelt introduced the term in 1933 as he pushed through Congress one of the boldest domestic agendas that the nation had seen, 75 bills in total, these important weeks in the early history of a presidency have become a lens through which politicians and pundits view the effectiveness of a new leader.
The Hundred Day record for presidents is mixed.
John F. Kennedy saw a Democratic Congress -- deeply divided between conservative southern Democrats and liberal northern Democrats -- stifle most of his domestic agenda, while the Bay of Pigs fiasco in Cuba undercut the perception that many Americans had of his foreign policy competence.
Ronald Reagan didn't get nearly as much done as FDR, as a Republican Senate could not overcome the opposition of a Democratic House, and in March the would-be assassin John Hinckley shot him, but the president was able to get a historic tax reduction moving through Congress and he deregulated oil markets through executive action.
Bill Clinton had an even worse experience than Kennedy, despite enjoying a Democratic House until 1994 and even though he had promised overwhelming success.
In his Hundred Days, President Obama moved his stimulus bill through Congress and put into motion the financial regulation proposals that would culminate in the Dodd-Frank legislation.
The truth is that the Hundred Days is just a construct, a way for presidents to define a specific period of time and to create pressure on allies in Congress to move as fast as possible before their time for legislating closes. It's interesting to note that some presidents who are considered failures, such as Jimmy Carter, actually had a bountiful Hundred Days.
The notion of the Hundred Days offers a way for the news media to create a sense of drama for viewers and readers by fashioning a clear narrative.
The entire premise rests on the belief that a president has some "political capital" he can use after an election to push things through Congress, a so-called "honeymoon" period when legislators will bend to his will. As every president discovers, these concepts are overblown and opponents are ready to fight in the first Hundred Days and thereafter.
What will President Trump do in his Hundred Days? For all the talk about his unpredictability and maverick style, the outlines of what we are going to see in this period are pretty clear. His inaugural address indicated that, once again, the Trump "pivot" will have to wait. While the details are fuzzy, and the devil is in the details, we can expect to see him work with the Republican Congress on a number of objectives.
Few issues have animated Donald Trump as much as deregulating the economy, particularly energy markets and financial institutions. It was not much of a surprise that the markets boomed after Trump was elected president.
After all, Trump is an ardent supporter of this core idea from the Reagan Revolution: removing government restrictions from economic activity is the best way to go. Trump has made it clear throughout his campaign that he views federal regulations as an inhibition to economic growth.
We should expect to see him push aggressively for ending the prohibitions on offshore drilling that have hampered oil exploration. With a Cabinet team picked right out of Wall Street, the administration will also work to either overturn or gut the Dodd-Frank financial regulations that were put into place after the 2008 crash.
Deregulation will not only occur through executive action and legislation, but also through the hands of potential Cabinet officials like Rick Perry and Scott Pruitt, if they are confirmed, who have no sympathy for the programs they are now responsible for administering.
Trump has made it clear that he is coming after as much of President Obama's legacy as possible. The first program on the chopping block is the Affordable Care Act, and the congressional Republicans have already gotten started by passing bills that eliminate most of the program.
If Trump follows through on his promise to gut the program, it will be difficult for Democrats to stop him. Yes there could be catastrophic fallout and a political backlash as millions lose their benefits, but right now it seems that Republicans are deciding that they will deal with that later.
Trump has also promised to go after other programs, such as the "Dreamers" executive action that allowed the children of undocumented immigrants who were born in this country to stay.
He might use his executive power to overturn what Obama achieved on issues like the Paris climate agreement, the Trans-Pacific Partnership, and the Iran Nuclear deal.
He will also likely go after lesser known executive orders, such as Obama's 2016 action instructing the Bureau of Alcohol, Tobacco, Firearms and Explosives that significantly broadened the term of who was "engaged in the business" of selling guns so to give the federal government greater regulatory power.
Trump won't only be focused on tearing things down. With a very conservative Republican Congress to work with, he will try to use this window to start creating a legacy of his own. Although we don't know if he will brand his programs with the Trump logo, we do know that there are a number of areas where he will pursue legislation that fulfills some of his campaign goals.
We are very likely to see efforts from the White House to make good on his hard-line anti-immigration rules. He might go for broke and push for the construction of a wall -- or else he might work within the boundaries of what's politically easier such as increasing deportations and putting more funding into border control. He is also expected to put forward an infrastructure bill laden with tax incentives for developers to show that he is serious about creating jobs while placing Democrats in a difficult position to oppose him. Another area where he could potentially attract Democrats would be a tax reform package that eliminates incentives for corporations to move overseas. Loophole-closing reform has often been an issue that can draw bipartisan support.
Nominate and confirm
President Trump has already started with this process. He has pushed hard and fast for his Cabinet picks, staffing the offices with members who if confirmed will push for a very conservative agenda. Some of the nominees might get tripped up, particularly on ethics issues that have emerged in the hearings.
The main problem is that Senate Democrats did away with the filibuster for nearly all confirmations in 2013, meaning that Republicans only have to get a simple majority of the Senate to approve nominees.
The most difficult battle will be the Supreme Court where the Democrats still do have the filibuster at their disposal. Trump has promised to make a very conservative pick to fill the vacancy that now exists, tipping the balance to the right. We should expect he will do that early on to build his support with the conservative base. The Supreme Court won't be the only selection. He will move to fill as many federal judgeships as he can with conservative justices to build his support with the right and with Senate Democrats now unable to filibuster his appointments.
Don't be surprised if Trump exercises presidential power with a show of force against ISIS. Throughout his campaign, the president blasted the Obama administration for being too timid against international security threats.
He criticized the administration for refusing to take forceful action when terrorists struck and for not doing enough in Syria to put down the ISIS forces fighting against the Assad regime. All eyes are now on the White House to see whether the president employs military force to respond to these security concerns.
He will reverse much of what Obama has accomplished by putting diplomacy and international alliances front and center. We should expect the continuation of provocative statements about countries such as China as well as the use of threats involving trade against countries he sees as hostile.
NATO will be tested more than ever with Trump's attacks on the alliance and potential support for Republicans threats to reduce our financial contributions. At the same time we should not be surprised to see an easing of sanctions against the Russians.
Of course, it's not possible to completely predict how the Hundred Days will shape up. Unexpected events have a way of reshaping the agenda of an administration, forcing the president to adjust and improve and to move in new directions.