I am pretty sure that liberal started to become a dirty word when Richard Nixon found he could win elections by lying about his opponents (Jerry Voorhees and Helen Gahagan Douglas). Then when he was President and decided that the policy of "benign neglect" would attract all the bigots to his party the negative connotation was then firmly established. So much so that Trent Lott(R -Miss.) could compliment Strom Thurmond (R -S.C.) on his birthday that had he (Thurmond) been elected president in 1948 would wouldn't have the "trouble" we have today.