Mexican Americans have been reliably Democratic since the Civil War. Granted, turnout was abysmal (and is still poor), but there has never been any significant pocket of support for the Republicans among Mexican Americans.
Why do you say that? While I don't agree with the OP (Mexican Americans were not solidly Republican until Nixon, of course), I don't think they were necessarily reliably Democratic after the Civil War. Traditionally Hispanic parts of New Mexico tended to vote Republican before the New Deal.
