Heresy St. Thomas (II-II:11:1) defines heresy: "a species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas... There are, therefore, two ways of deviating from Christianity: the one by refusing to believe in Christ Himself, which is the way of infidelity, common to Pagans and Jews; the other by restricting belief to certain points of Christ's doctrine selected and fashioned at pleasure, which is the way of heretics."
I can almost guarantee that Chaput won’t do a thing to stop pro-infanticide politicians from receiving Communion during the convention or thereafter.
This is news to me, as is the same-sex marriage support. In fact, it looks like Ritter's backed off from reports of his support for SSM, falling into the unsustainable "domestic unions" compromise also favored by McCain.
I once saw the archbishop try to temper intense pressure from anti-Ritter Catholics at one public gathering by saying Ritter had done some good things on conscience protection.
The rationale is that danger to the RCC to be seen meddling in politics is worse than allowing the scandal. That is, IMHO, a ridiculous bit of double-effect cheese-paring and a direct affront to the Pope.