Eric Scheie over at Classical Values talks about why Thompson isn't going to get the religious conservative vote, because of his reluctance to pass an amendment defining marriage as one man, one woman, or to prohibit abortion. Thompson, of course, wants judges to do their job--which isn't finding a right to same-sex marriage or abortion hiding inside the Fourteenth Amendment.
I know that there are religious conservatives who aren't happy with Thompson for these reasons. But my view on this very simple. Freedom of state governments to make their own decisions (unless clearly contrary to the state or federal constitution) is a fundamental conservative principle. Sometimes the results are unfortunate (Oregon's euthanasia law, California's medical marijuana law). But I would rather have 50 states making their own decisions, even if the results are sometimes flawed or stupid, than have the federal government impose its will. A government strong enough to impose one morality is strong enough to impose one immorality.
Or to put in more direct terms: a federal government with authority to prohibit the state legislatures from recognizing same-sex marriage also has authority to require state legislatures to recognize same-sex marriage. A federal government with authority to ban abortion in every state also has authority to require every state to allow and fund abortion.
If we reach the point where 2/3 of both houses of Congress and 3/4 of the states are prepared to amend the Constitution, fine, we can talk. But any religious conservative who thinks that we are even close to that level of unanimity needs to get out more.