Trump is wrong about a lot of things — especially the notion that he's been a successful president so far — but maybe the 100-day standard for a president doesn't make a great deal of sense to begin with.
Aside from Franklin Delano Roosevelt, whose first 100 days in office transformed the executive branch and began the slow process of bringing about an American recovery from the Great Depression, most modern presidents have not had their first hundred days turn out to be particularly noteworthy. The only one who comes close, Ronald Reagan, used his first 100 days to set up the revolutionary changes he planned on making to reduce the size of the federal government. But very few of those policies were officially passed during that period. Even Reagan didn't pass 15 landmark bills in his first 100 days, like FDR managed to do.
But considering that Trump insists on bragging about how his opening days as president surpass those of any of his predecessors — and considering that, despite this bluster, his own press secretary can't name a single legislative achievement since his boss took office — it's worth noting how Trump's opening days pale in comparison to those of the man who served immediately before him, President Barack Obama — a popular target of the pre-presidential Trump.
It's easy to forget this now, but when Obama first took office in 2009, his critics were quick to claim that he "hadn't done anything." But it was during this period that Obama, like Roosevelt before him, pulled the economy out of crisis by passing a comprehensive stimulus package. Although the stimulus bill of 2009 wasn't as innovative as the measures implemented by Roosevelt in 1933, it managed to set America on a course toward eventual economic correction after the devastation wrought by the crash of 2008.
It was also during this period that Obama signed the Lilly Ledbetter Fair Pay Act, approved a troop surge in Afghanistan, and simultaneously began the official wind-down of the Iraq War.
While Obama's critics liked to complain that none of this was revolutionary, they forget that Obama always presented himself as a moderate-left figure rather than an ideologically pioneering one. By the standards of a Bernie Sanders-esque socialist, Obama's first 100 days were a deflating disappointment. On the other hand, by the standards of a centrist with a practical view on what the government can and should do, a president who saved the economy from the worst crisis in generations, dealt a blow to systemic economic injustice, and escalated a necessary war while winding down a bad one deserves a lot of credit for his successes.
By contrast, Trump has very little to show for his first 100 days. A missile strike in Syria certainly surprised the world and rattled a few chains, but it doesn't seem to have been part of any coherent shift in American foreign policy. His attempts at imposing a travel ban on several Muslim-majority countries, repealing Obama's health care reform bill and getting started on a U.S.-Mexico border wall have all been miserable failures. Indeed, the one lasting achievement that Trump can brag about right now is nominating Neil Gorsuch to the Supreme Court — but the fact that he was able to accomplish that in his first 100 days has everything to do with the Senate Republicans' obstruction of Merrick Garland last year, and nothing to do with Trump himself.
As Trump should have learned from the musical "Hamilton" — maybe Vice President Mike Pence could give him a synopsis — "Winning was easy, young man. Governing's harder."
Trump has an undeniable talent for self-promotion, for someone whose job it is to lead the free world, no amount of bloviation can conceal a failure to deliver the goods. It may not be fair that presidents are expected to achieve so much in their first 100 days, but the standard at the very least can help us engage in some useful side-by-side comparisons. One point it makes perfectly clear is that, while Obama was no Roosevelt, Trump is nowhere near being as competent or successful as Obama.