They rely on the liberals for the money to run for reelection ala Senator Evan Bayh.
The states need to pass laws that their representative can only use money collected from citizens in their respective states.
And what good would that do?
In the early 90s several states enacted term limits for their state and Federal officials. The affected “esteemed gentlemen and gentlewomen proceeded to sue and the courts ruled that the laws were un freaking constitutional. The only way to control out of state contributions is for THEM to enact laws to control it. FAT CHANCE.