The Republican party is currently losing about 1% of its voters every year, because they are dying. They are not changing party or voting differently. They are passing away. Joining the choir invisible. This is hard for a party to fix.
The only hope I see for them is to raise their voters from the dead and train the zombies to vote Republican. It should be easy to do. Zombies seem like a natural constituency. They hate government, avoid health care and never pay taxes. It might work.
Just trying to help. (with a tip of the hat to Petronius Jones)