Trump is either on to something with the election fraud or he isn't. If he isn't, he'll look a schmuck. If it turns out he is, and there is strong evidence that he might be from some reports, then the people who've been shouting "no way!" will look silly and it will be pretty devastating to dems.
Of course he will find wide spread "voter fraud"! He said so on the ABC 20/20 interview himself!
People who are dead and registered (because people die)! People who are registered in two states! (like his entire staff seems to be).
He will conclude all of these people must have voted HRC. He is already spreading lies (yes, lies!) about people who have told him they were standing in line with south-Americans (he know they were!) and then told to leave the line. This too will be believed to be true (I very much hope you will read this piece)
Then a few cases of genuine voter-fraud which can be stamped up (someone tells someone to vote for him, whatever, this happens every year in our elections) will be found an paraded around as "evidence" every single dead registered voter voted liberal.
Don't believe me?
The "the election was rigged" meme is already being spread as true on the alt-right twittersphere if you look into it using the usual lines: "You are just mad because you lost the election even though it was rigged".
Breitbart is going to support this claim, or rather, how important that investigation is. It will then find a number of double-registered voters and dead voters (even though there is no evidence actually false votes were cast) and THAT will be used as a line to further de-legitimize THAT aspect of the american democracy as well.