People forget his "Hard Right" phase which coincided with the 1994 Gingrich win. There may be some things Frum won't do, but most things are negotiable for him if it advances his career.
I was going to call BS on your anti-RINO diatribe, but in actual fact more Democrats did vote against the 1965 Immigration Act than Republicans.
So you're right: it's not something that the GOP moderates (which by today's standards included most of the party after Goldwater was defeated) can blame on Democrats alone.
But you will find that even Reagan didn't do much against even illegal immigration. The lure of cheap labor is a lot stronger than party or ideological divisions.
I concur, that's been the case for eons, going back to, well, Lincoln .... It was the Democrats who reformed immigration and stopped the wage-breakers' game in 1925, and LBJ who engineered the party's volte-face in 1953/4, which was motivated by LBJ's knowledge that Mexicans tend to vote Left and are generationally tenacious in their voting patterns. Even on a showing that the Democrat Party militates against their many social interests, they vote for the Left Party as the party of subsidies and price/rent control, largely because great-grandfathers Triunfador and Sotero did so.