I would think, that given Trump's delusional ego, that there were recordings of Trump's infamous encounter with Comey. Given that the current technology is so advanced, a device the size of a fingernail is all that is needed to record audio. Again, such devices could easily be encrypted and then deposed of as easy as swatting a fly, lighting a match, or flushing the toilet.
Given all the knowledge of Nixon's mistakes, it would be child's play to insure that no one would even know for certainty, whether anyone at any time, anywhere isn't being recorded visually or recorded by an audio device, and that information could just cease to exist.
Given the vast resources that Donald Trump has as a business mogul and President, and his demeanor of being many personalities, there is simply no way to corner this shape-shifter.