To stave this off - as I have suggested before - conservatives need to move
en masse to the Democratic Party and start electing conservative Democrats everywhere possible. This will short circuit the messaging you just listed, immediately render useless the billions the Left has spent tarnishing the GOP's image, and attract large numbers of black and Hispanic voters who like some conservative ideas but always fall for the anti-Republican spin. If conservatives are serious about stopping the slide, this is the best way to do it.
In effect, we have only one party now - so what difference does the label make? We would make more progress in a Democratic Party with two factions than we are currently making with our old, damaged GOP brand.
That is one way of doing it, which I have actually considered briefly, but we haven’t been able to make that work with the GOP, so I see no reason to expect it to work any better with the DNC. Besides, then we would be in the position of associating ourselves with Nancy Pelosi and others of her ilk.