DoJ under Trump needs to sue California to stop this illegal vote harvesting practice. They throw out Republican votes and only deliver Democrat illegal alien voters. This needs to be addressed now so it isn’t a big issue in 2020.
That is one part of what needs to be done. Litigating may take more time than we have before 2020, though. Would have to get the SC to take it up quickly. And then what? What do we ask the court to do, legislate a fair process for the state? Replacing the state scheme would require a huge rewrite of what they have now. Get rid of motor voter (a federal law, that the House would have to agree to get rid of). Then put in place controls to prevent illegals from voting. Then get rid of voting in advance. Then get rid of absentee ballots except for specific situations requiring it, attested to by the voter and subject to examination. And many other things.
Completely revising this entire California scheme is a big challenge. With a Republican house not led by Paul Ryan, you could have maybe passed a law that applies to federal elections that prevents this sort of shenanigan. But now, that possibility is gone for 2 years. Can you get such a law by executive order? I doubt it. Maybe some protections, but not elimination of state law. Yet something must be done before 2020, or they will steal it. The highest tech minds and politically corrupt officials have been working on this plan ever since they screwed up in 2016. They are determined to stamp out our little temper tantrum (i.e., democracy). We have to be even smarter, and we are already behind the 8 ball.