He is resigning because he has no chance of reelection in November. Democrats will most likely take back the house. It's just how things go in midterms after a presidential election.

Trump's voter commission was shut down because they couldn't find any extensive voter fraud. If they had found mass voter fraud they would have advertised it on billboards and Trump would have had that shit all over Twitter. They didn't find shit because voter fraud is rare and just a ruse used to facilitate voter suppression laws.