It's like how Lincoln was a Republican and set the slaves free, despite modern day Republican policies are anti-foreigners/ethnic minorities. There's a law in Arizona which states that any "foreign-looking" person can be asked for their documents.
http://en.wikipedia.org/wiki/Arizona_SB_1070
The Conservatives, our right-wing party, have modernised their policies and are now in favour of abortion, homosexuals and anti-corporal and capital punishment. The Republicans haven't because they believe the US constitution should be interpreted in what the Founding Fathers intended, as well as having strict interpretations of the Bible.