Gerrymander, voter suppression, disenfranchisement, electoral violence. And, if necessary, straight-up fraud.
US electoral systems were already infamously corrupt pre-Trump. The red state legislatures have spent the last few years intensifying those factors as fast as they can, and they still continue to do so. Electoral rolls are being purged, districts are being redrawn, polling locations are being shut down.
Any significant legal challenge to this is going to eventually end up at the USSC, where it will be ruled upon by Kavanaugh/Gorsuch/Alito/etc.
