This Gallup poll from November 2016 asked the question:
" Now that Donald Trump has been declared the winner and will be inaugurated in January, will you accept him as the legitimate president, or not?"
On the same page, Gallup reports of asking the same question following G.W. Bush's election.
My question: Do you know of any dataset containing answers to a similar question, but for more than two elections?
In the best of worlds, I would be looking for a panel dataset where the same people are asked the question across several elections.