[Presto]

I've been wondering about that myself. But I suspect that unless an ad instructs you how to vote that it cannot be blocked. Just a suspicion.

[July 4th]

But I suspect that unless an ad instructs you how to vote that it cannot be blocked

The rules have changed. Campaign finance reform sets a 60-day all-out ban on "electioneering communications" by outside groups. It doesn't matter what they say - it's blocked. The only money that can be spent is money that was donated directly to candidates or registered PACs. Money going to those organizations is carefully cataloged and limited, a.k.a. "regulated."