Should Church leaders be advocating that their congregations not vote for any politician who supports...?

Very sticky issue, because under current law, it is illegal for a tax exempt entity to actively endorse one candidate or another, as part of the "separation of church and state" interpretation. It is in violation of the tax exempt laws for example for a minister or priest to say " Do not vote for John Kerry because he supports abortion". It is not illegal to say "Our church believes Abortion is a sin, and it is the duty of our members to insure that our leaders understand this. Ther is no more important issue than the stance on abortion". The difference is semantics, yet very important.