I would submit, small election rigging is easier to investigate. Also, you wouldn’t want to give up the gameplan on 1 local election.
Election rigging is about effecting the margins. 1/4 here, 1/2 point somewhere else. Also, national elections have multiple chokepoints you can tamper with. Closing polling places, changing early voting rules. Do you really think Trump’s current stooge playing postmaster general is beyond separating out ballots and effecting their delivery. They’ve already changed the postmarking date rules. Trump tried to seize voting machines in 2020 and now he signed an E.O. stating he can use the military to steal voting machines. You could say courts will stop this but as SCOTUS has shown you have to wait for something to happen before taking it to court. Meanwhile Trump causes the damage, and it takes too much time for the courts to settle the case.