Catholic Politicians: Allegiance to Church or State?

This business between Patrick Kennedy and Bishop Tobin over abortion and the health care bill is becoming a real tempest in a teapot, exacerbated by the fact that Bishop Tobin is no wallflower and has no qualms about arguing in public, which he does rather well. Of course, based on the public record, it appears that it was Kennedy himself who took a private matter public in the first place, something I am sure he wishes he hadn't done. Now we have this bizarre crossover of the issue into Kennedy's mental state and fitness, despite the Bishop's assurances that he means no such thing.

There is one critical aspect of this controversy that I don't understand here (disclosure: I am not a Catholic)- Are American politicians supposed to obey the Church first and foremost on a particular issue and not their own consciences or the prevailing view of their constituents? If that is the case, aren't we back at the charge that presidential candidate John Kennedy had to challenge: that as a Roman Catholic he would be doing the bidding of the Pope?

The Church's position seems to be: obey us or leave the Church. If a Catholic politician has to obey his Church, isn't that a case of church interference into affairs of state? Is it right for the Catholic Church, or any church or religion here in America, to demand that allegiance of an elected official?