The presidency of the United States is a mighty office, and the weight of it has shaped many men. The best among them have had the breadth of mind to set aside fixed tropes, face the world as it is and allow both the exigencies of leadership and the potential for America to do good to guide them. Others have been prisoners of their own dogma and bequeathed to their successors a world of trouble.
The question, then, is which man is Mr Donald Trump?
On foreign policy, candidate Trump promised little ideology and plenty of anecdote-driven reactionism. Not enough jobs? Get them back. Terrible Iran deal? Tear it up. Allies free-riding on US defence largesse? Send them a bill. Fighting unnecessary wars? Stop. Far from a doctrine, Mr Trump offered a smorgasbord of retorts and one-liners that added up to what many worried would be a dangerous isolationist and protectionist era in US politics.
But 100 days into his term, President Trump has been far more conventional than many dared hope. Many of his promises, from labelling China a currency manipulator to staying out of Syria and making nice with Russia, appear to be on hold - which should surprise no one.
Consider each recent president and contrast the candidate with the man in office: Mr George H.W. Bush promised a more "realist" global posture than Mr Ronald Reagan, but ended up proclaiming a "new world order". Mr Bill Clinton rejected that, insisting it was "the economy, stupid", but ended his tenure with his secretary of state arguing that the US is "the indispensable power". Mr George W. Bush promised a more "humble" presidency but, after 9/11, invaded Afghanistan and Iraq, inaugurating a far-from-humble "freedom agenda" to promote democracy in the Middle East. Mr Barack Obama promised to "end this war" in Iraq and wrap up the conflict with the Taleban, but joined Nato in invading Libya, recommitted troops to Iraq after withdrawing them, continued the war in Afghanistan and sent special operations forces to Syria and Yemen.
In short, the foreign policy promises of presidential candidates are rarely gospel. The world has a way of upending even the best-laid campaign platforms. And so, despite telling Mr Obama to "stay the hell out of Syria", Mr Trump blasted an airbase used for a chemical weapons attack on Day 76 of his presidency. He has overturned Mr Obama's non-policy of "strategic patience" with North Korea, recognising that Pyongyang has used the past eight years to advance its nuclear and missile programmes to the point of threatening the continental US.
On foreign policy, candidate Trump promised little ideology and plenty of anecdote-driven reactionism... But 100 days into his term, President Trump has been far more conventional than many dared hope. Many of his promises, from labelling China a currency manipulator to staying out of Syria and making nice with Russia, appear to be on hold - which should surprise no one.
Mr Trump has sent his Secretary of State to tell Russian President Vladimir Putin to drop Syrian dictator Bashar al-Assad, recommitted to Nato in the face of growing Russian predations, confirmed Iranian compliance with the Joint Comprehensive Plan of Action and otherwise behaved like - dare we say it - a normal president. And, though Mr Trump has stuck by his pledge to withdraw from the Trans-Pacific Partnership, he also indicated he will pursue bilateral trade agreements, a far cry from a reversion to Smoot-Hawley some feared.
Where Mr Trump has neither flipped nor flopped is on his strident anti-refugee, anti-immigration posture. The President followed through on pledges to limit immigration from states of terrorism concern, to put in place "extreme vetting" and to ban refugees from Syria. While implementation of those executive orders is suspended pending litigation, the White House appears bent on staying true to that campaign promise. Similarly, Mr Trump seems as uninterested as President as he was as a candidate in picking personal fights with foreign despots, such as Russia's Putin or Turkey's Recep Tayyip Erdogan.
So, after nearly 100 days, what more do we know about Mr Trump, commander-in-chief? Is he settling into a more nuanced security policy, guided by the likes of Cabinet members Jim Mattis and Rex Tillerson and advisers Gary Cohn and H.R. McMaster? Or is this only a temporary blip before other factions in the White House pull the clearly mercurial, impulsive leader back to fulfilling his hyperbolic campaign agenda?
All we know now is what we see and do not see. What we have seen from Mr Trump in his early days as President is a man who is owning his burdens, one who wants to rebuild the deterrent power of the US, one who is shocked by the horrors of war and one who is game to push back on enemies. All to the good.
But what we do not see is a man who is game to threaten other leaders' personal power, namely Mr Putin and Mr Erdogan. Nor, most importantly, do we have a sense of his world view or the policies that underpin his initial tactical steps. On national security, at least, it will be those policies, and not the occasional phone call or air strike, that will make or break this President in the world.
•The writer is senior vice-president for foreign and defence policy studies at the American Enterprise Institute.