At the moment, a substantial percentage of US citizens reportedly believes that the outcome of the 2020 presidential election was substantially affected by fraud of one sort or the other. (NOTE: whether or not those persons are correct is completely off-topic for this question)
The main reason for these beliefs is a series of unproven claims made by the incumbent president (Donald Trump) and his staff.
These claims are now so widespread that they form a political movement in their own right, whether or not the actual claims have any truth to them, thereby seriously affecting politics in the coming year by undermining the respect for elected officials and their decisions. Conversely, the number of people believing that the election was indeed correct (an even larger number) forbids any concession to the fraud-believers.
It seems to me like there are only two ways that any government can gain full legitimacy in the eyes of the people in such a situation:
Either (supposing that the election actually was skewed by substantial fraud), those claims of fraud are proven and confessed, the apparent winner resigns in shame after which a new and presumably fair election takes place.
Or (supposing that the claims of widespread fraud are without merit), said claims must be unequivocally renounced by the incumbent/former president, effectively admitting that they were lies or at least gross exaggerations.
So, is there any way to force an incumbent or former US president to account for sweeping claims of voter fraud under oath (and threat of perjury)? To either state on record that the claims were groundless or present actual proof?