I remember the Reagan era well as I supported him all three times for President. I don’t recall anyone having a problem with Reagan switching parties as he did so in 1964 (to support Goldwater, if now before). He didn’t switch parties (as an opportunist) to run for President.
Reagan’s opposition came from the Rockefeller Wing of the GOP (which is today known as the Bush Wing of the GOP, and attacks true conservatives).
I know he didn't. But those republicans that bashed him for even thinking about even running for President used that as an excuse to try to destroy him which was their way of bringing their own candidate up in the polls.
They used the liberal approach which is destroy the other guy so my guy looks good rather than focus on bringing up their guy to be able to go against the one they opposed. End result? Their candidate never went up in the polls because they kept the spotlight so much on the republican they attacked they forgot to put the spotlight on their own candidate.
The Newsmax poll just released (which mirrors very closely to another poll released a few days ago) suggests that's happening again.