It doesn't need to be a long investigation, but reopen the Watergate investigation. We still don't know why the five or so burglars broke into the Democratic Party offices. Some of them are still alive. Call in as many of those involved from Watergate as are still alive, and ask them to come clean.
It needn't be a long investigation. But, call them into a congressional hearing, and plea in the name of patriotism for them to come clean. Once they've all died, their secrets may well be lost. What is the saying, Dead men don't talk? The living years are when secrets can be revealed. We should call the participants in before they are all lost to their graves.