Sure they can be a Christian ... just like the Bible says in Romans!
Romans 10 ...
8 But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith which we preach):
9 that if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved.
10 For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation.
11 For the Scripture says, “Whoever believes on Him will not be put to shame.”
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Being a Christian doesn’t mean that you know it all, get everything right, or are right about even other things in the Bible (I know a lot of Christians wrong there) ... but a person is a Christian on the basis of what the Bible says ...
If they have accepted the real Christ and rejected false ones, they have set upon a path which will lead them away from support of abortion, homosexual behavior and worship of government.