What Citizens United hath wrought:
Both incumbents and potential challengers realize that a deep-pocketed PAC could decide their race. So when they get a call from that PAC’s director urging them to support this or that, they’re that much likelier to listen. The result, then, isn’t just that moneyed interests can throw congressional elections. It’s that they wield more influence after the election — and they can exercise that power without spending a dollar.