It certainly was legitimate in the ordinary meaning of the term. Hillary Clinton won three million more votes than Trump but Trump won more states, and in a federal system that can happen.
Trump's victory was perfectly constitutional and in strictly legal terms legitimate. But "legitimacy" has a wider meaning in politics, referring to the general recognition that the election was fair and the result can be respected.
This was the legitimacy that Trump himself challenged when it looked like he was going to lose, so he can hardly complain some Democrats have not accepted Clinton lost fair and square.
They cite the FBI director's unfortunate decision to re-open its investigation of her emails very late in the campaign, and the disclosures since of suspected Russian attempts to influence the result.
Excuses for failure can always be found but these did not stop Clinton winning the popular vote. Democrats must respect the result in the electoral college.
This sort of debate is normally settled long before Inauguration Day. The fact that it has persisted so long this time is largely Trump's own fault, for he has not observed the usual protocol of transition.
Immediately after the vote, he set out on a victory lap of crucial states, rousing his supporters again. More ominously, he broke the rule that the US must have "one president at a time".
Through the transition Trump repeatedly issued comment on events that was still properly the role of President Obama. Trump's disrespect for this convention of presidency leaves little doubt he will have no patience with many others.
The fact that his comments, usually on Twitter, were hasty, ill-considered and clumsy does not bode well for the next four years.
Nor does his propensity for threatening and ordering American companies into line, which he did several times during the transition.
Everything he has done so far confirms the character he displayed in the campaign.
America has elected a bully and a narcissist who is too easily flattered and too easily provoked.
But Inauguration Day might yet show he can raise his sights and rise to the standards of the office he has won. We can but hope.