Once upon a time the GOP was a coalition of Wall Street and Main Street business interests.
Nixon’s Southern Strategy in 1968 opened the GOP door to a Star Wars bar scene of obscurantists, chiliasts, gun fondlers, racists, cross huggers, and paranoids.
There are sufficient individuals in the US electorate who identify themselves with one or more of the above categories of enthusiasms to cobble together a loose political coalition. The problem becomes serious when voters contemplate the horrible possibility of a representative of these atavisms polishing his trousers seat on an Oval Office chair.
The remaining sane Republicans got a taste of this appalling state of affairs during the Bush II era. Once bitten, twice shy.
Republican victories before 1968 in a handful of southern states doesn’t equate to a “southern strategy”. The term actually “southern strategy” refers to dog whistle politics of racism. Eisenhower and other pre-Nixon Republican aspirants to the presidency never stooped to pandering to white racism. Nixon did. Before Nixon, most enfranchised southern Blacks voted GOP. Even though LBJ’s civil rights acts vastly increased the size of the Afro American electorate, they deserted the GOP en masse, recognising correctly that the mantle of white racism had been wrested away by the Republican Party from the Democrats. Simultaneously, white Southern racists deserted the Democrats and voted for the GOP or for George Wallace.