About as much as the July "no reasonable proscutor would take the case" announcement did.
It will be interesting if Trump adapts this Minneapolis speech to account for the letter. He did good to not "take the bait" and make additional accusations. All he did was praise Comey for reviewing the evidence. Now that he's reviewed it and doubled down on the lack of criminality for having a private server with classified information on it, Trump is back to the old stump speech, without the "praise for Comey" part. Comey is back in the weasel cage!
Good point,C.
Trump can certainly make the case for the rigged system in DC, that has circled the wagons to protect Hillary.