This is the Big Lie of the pro-abortion "Catholic" politicians. The fact is that the Church teaches that "legal" abortion is an INJUSTICE--i.e., it is a public policy that is unjust, and therefore morally evil, and therefore every Catholic is strictly required to oppose it. There is no question of public vs. private "beliefs" about abortion, because "legal" abortion is not a private matter. Saying "I oppose abortion, and therefore would never have one myself, but I support keeping abortion legal" is precisely the same as saying that Hitler was a good Catholic because he PRIVATELY opposed the building and operation of Auschwitz, but wanted others to have the choice to work there.
I may be forced to accept Roe v. Wade because it's the law of the land but that doesn't mean I need to either promote it or agree with it. I also believe that the whole render unto Caesar thing pretty much requires that I obey the law and don't shoot abortion doctors because they're baby killers. On the other hand if the government demanded that I commit an unjust killing and I tell them to go to hell then no problem. All this tells me is this person doesn't really embrace this particular Catholic teaching.
Justice Scalia gave a very good argument which I believe applies to this case but it had to do with the death penalty. In his argument, if the church actual oppossed the death penalty instead of recommending against it he would necessarily have to recuse himself from judging any death penalty cases. The same legal principle is involved here, and the churches stance here regarding the prohibition of abortion isn't a recommendation, it's exactly that, a prohibition.