So many here, judging a man's faith, propping themselves up as the arbiter of who is really Christian and who is not.
You're right, none of us should be judging another person's relationship with God. However, when he says he's a member of a particular church - but isn't - that's not judging his faith but his truthfulness. He could be a good Christian even if he didn't belong to a particular church, but why not just tell the truth about it?
Jesus said, "Beware of the false prophets, who come to you in sheep's clothing, but inwardly are ravenous wolves. You will know them by their fruits. Grapes are not gathered from thorn bushes, nor figs from thistles, are they? Even so, every good tree bears good fruit; but the bad tree bears bad fruit. ... Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven; but he who does the will of My Father who is in heaven." Matt. 7:15-17, 21.
I think it's fair to look at
any person who claims to be a Christian, whether Trump, Kerry, Cruz, Obama, your cousin or anyone else, and evaluate whether they produce good fruit (what can be observed from their words and actions) or bad.