Litmus test.
Normally, I'd certainly agree with you. However, I believe that "Christian" implies living the philosophy taught by Christ.
Calling oneself "Christian" and ignoring the Sermon on the Mount, for instance, is doing a disservice to Christ, and is only done by people more cynical than I.
The test is to apply the red print (the words of Christ) in the Bible with the actions of professed "believers". If they don't match, that person is "Christian" in name only, attempting to live in the aura of that great personage for their own base reasons.
Goes not only for politicians. And I'm not dissing Christ, at all, even a little bit. He's one of my heroes.
Hope that helps.
Arf