And in light of what has happened in California under Arnold Shwarzenegger, I don't know how any Republican could think that compromising principles to support a candidate simply because of his party affiliation will make any difference at all.
What has happened in California really doesn’t apply here. The party affiliation of the President of the U.S. matters. Democrat presidents tend to be more liberal across the board than Republican presidents.
If Hillary is elected President and if the Democrats keep control of the Congress, her health care plan will be passed because the Democrats will think that the country has moved leftward and that it has given them a mandate to implement liberal laws.
It is all well and good to talk about standing on one’s principles but abstaining from the election because the Republican candidate isn’t “pure” enough or conservative enough will only ensure that the Democrats win and this will just set the conservative cause back for years to come.