Yes, it is absolutely necessary in the eyes of God the Father that Catholic priests, Orthodox clergy, and Protestant preachers preach against voting for pro-abortion politicians in any party because abortion is baby killing.
Voting for pro-abortion politician is voting for baby killing, and God will hold that voter responsible for the killing of the innocent babies.
Jesus Christ addressed politics of His society in preaching and constantly preached for the advancement of the Kingdom of God on earth.
It is necessary for Christian leaders to provide specific guidance to vote against pro-abortion politicians in their Sunday preaching, because this is what God wants.
God wants Christians to make disciples of nations, and this happens by changing laws to follow God’s Law.