1
1) I consider Trump an independent and an opportunist -- not unlike Bill Clinton in that respect.
1a) The reason is stated by Glenn Beck (who is not my favorite analyst). A 21st-century Republican, for me, is one who authentically believes in the vision of the Founding Fathers, and the Constitution, and who won't negotiate that principle.
2) People vote Republican for different reasons. Evangelicals are very different from those who vote Republican because of money issues. Who are different from those who want to avoid an Islamo-Europe West.
3) No. GOP voters will poll based on what they see as the greatest threat to our heritage: humanism, or immigration/terrorism/gerrymandering, or the welfare state, or whatever.