It is not clear that Newt Gingrich will be the Republican party’s presidential nominee, much less the next president of the United States. But asking the question about a “Catholic president” sharpens what “Catholic” means in politics.

One becomes a Catholic by Baptism, obliged to observe the commandments of God: do not lie, steal, fight, or commit adultery. Catholics are also supposed to go to Mass on Sundays. Mr. Gingrich qualifies best for the first and the last practices on this list, with a dubious record for the in-betweens. He has been rejected by his party for unethical behavior, married three times and twice remarried. Many in Catholic America can not understand why Mr. Gingrich was able to have his third marriage recognized by the church. But John F....