I've got a theological question for you:
What would be the theological rationale behind a bishop's telling a Catholic politician not to take communion, as long as the politician will not change his position on abortion rights?
"It is related to the canonical prohibition against being an accomplice to an abortion. See for a discussion."
Then I though, well, a more theological answer would refer directly to the sin of scandal, which, according to the CCC means "an attitude or behavior which leads another to do evil." (CCC 2284). Notice that scandal itself is a sin against the fifth commandment! You should read the whole discussion of scandal at this point. Even if a politician weren't interpreted as an accomplice in the canonical sense, he would still be guilty of the sin of scandal, and it would be a grave sin indeed similar to, if not exactly falling under Canon 1373!