WASHINGTON (CNN) The frontrunner for the Republican presidential nomination is a former pro-choice Democrat who once supported Canadian-style universal health care, tax hikes on the wealthy and said Hillary Clinton was "terrific." As he prepares for the first GOP debate of the election season next week, Donald Trump is disavowing many of his former positions and earning support from about one in every five Republicans through a combination of blustering rhetoric and dogged condemnation of the political class.