This is nothing but another attempt by Trump to obstruct justice.
If the investigation wasn't finding anything, why would they bother?
If the investigation is finding things, then does it matter why it was started?
Oh, and don't forget that Rod Rosenstein, who Trump appointed to Deputy Attorney General, is the guy who appointed Mueller to the investigation saying:
"My decision is not a finding that crimes have been committed or that any prosecution is warranted. I have made no such determination. What I have determined is that based upon the unique circumstances the public interest requires me to place this investigation under the authority of a person who exercises a degree of independence from the normal chain of command."
If Trump is innocent, the investigation will find that.