Fixing the electoral system so you could actually vote them out would be a good start. By fixing, I mean un-rigging.

It used to be that Senators were chosen by the state legislatures to represent the interest of their state. Having them directly elected by the people of each state seemed like a good idea at the time but it turns out what it actually did was give more direct power to the federal legislature and ended up taking away the state's influences on the federal government. And it increased the number of political electoral campaigns (as you now have people running for senate) and hence increased the number of ways that politicians can be bought and paid for. I'd say it looks like having senators elected directly may have actually been a bad idea in the long term.