This is a state problem. The national GOP can only support the state GOP in reforming election laws.
DeSantis curtailed ballot harvesting and many of the loopholes exploited by leftist groups to collect ballots during the election.
But most of the remaining states that need cleaning up (Pennsylvania, Michigan) have Democrat governors who will veto any repairs to the election system.
What you say is very true, it is a State problem and as you point out, the States with the biggest problems are the States with Democrat Governors.
What compounds the problem is that in these States, not only are the Governors Democrats, nearly the entirety of their States Governments are operated by Democrats. In those States, the Democrat Party has become the “Party of Government”, or perhaps to put it better, they have morphed into the “Government Party”.
What does that really mean? It means that the “Government” adopts policies that benefit and further entrench the “Government Party”. It also means that the Party operatives and contributors take first place among the hogs at the trough which further funds the Party and the Government.
When this happens as it has in places like Illinois/Chicago, productive business minded people simply leave the State/City leaving no one left in those jurisdictions except those who are benefited by the Government and the Government Party.
I literally see no way out for these States/Cities.