You can. It just takes an amendment to the Constitution.
I'm not against them per se, but I just don't think they will address the issues of corruption. In fact, it may accentuate them. You will have more lame ducks, who don't care if they fly in the face of their constituents, and may play right into the hands of corporations and lobbyists who will see that they are comfortable after leaving office. Much like now, except it will occur more often.