How do you deal with a president who won't answer legitimate questions?

Here's a good example of just why it's so difficult to take Donald Trump to task over the various mistruths and barefaced lies he routinely peddles.
Case in point: Trump's repeated claims that he somehow inherited "broken" COVID-19 tests from Barack Obama. When asked in a CNN interview yeaterday how it was possible for the Obama administration to have developed COVID-19 tests three years before the novel coronavirus was even discovered, all Trump does is to repeat over and over again, "We started off with bad, broken tests and obsolete tests ... We had broken tests. We had tests that were obsolete. We had tests that didn't take care of people." Regardless of the fact that some of it doesn't actually make sense, at no point does he even try to address the interviewer's point, which was put quite succinctly, "It's a new virus, so how could the tests be broken?"
If he doesn't answer legitimate questions, but merely parrots the same non-sensical tropes, insofar as they serve his own re-election purposes, then what else can you do? What Trump is doing is making a political calculation: he just doesn't care what liberal "fake news" outlets like CNN, and the kind people who watch them, think; he is much more concerned with hammering home his message to his own core supporters.
"Broken"? I'll say. The longer Trump remains in power, the more democracy dies a death of a thousand cuts. Never has there been such a cynical politician in a position of such power and influence.