I think it was inappropriate for him to stress this, and that it undermined his legitimacy and the legitimacy of the investigation. It isn't the job of an investigator to "exonerate" people that havn't been charged or prosecuted for a crime.

As far as I can tell all these comments did was validate his supporters beliefs that the investigation was a politically motivated attack, and simultaneously served as a psychological "out" for his detractors that were convinced he was in cahoots with Putin to undermine the country. Widening the divide between 2 sets of people that really ought to reconcile.

Disclaimer: I am not american, so this is an outsiders perspective.