If you have the relevant social conditions to support good government -- competent media, engaged citizenry, civil society groups that can form the basis of electoral coalitions, a political culture that values honesty -- then a politician who engages in a lot of shady behavior is likely to find himself voted out of office whether or not the shadiness in question is formally illegal. Conversely, absent adequate social conditions even the most admirable legal framework becomes a dead letter -- nobody investigates violations and/or nobody cares. At the end of the day there are always going to be loopholes in whatever scheme you create. You see good government when and where the citizens want it and are able to punish those who don't give it to them.
See also Timothy Burke:
The key priority is to rebuild the way the federal government actually functions in both its everyday and extraordinary business... the whole point of the U.S. Constitution [is] that it is an uncommitted, non-partisan prior constraint on the uses of governmental authority. If it turns out that its guarantees rest not so much on its formal provisions, but just on men and women of good will and honest commitment agreeing to live up to their responsibilities under the law and the social contract, then that’s what we need to work to rebuild and restore. The last eight years have been a test, and a lot of people, some of them surprising, failed it. Equally, many people in all parties and factions passed, which is also worth a lot of attention. A lot of the downward momentum has been arrested by people with whom I strongly disagree on political positions, but whose dedication to their office and responsibilities I appreciate. Much of what we know about what has gone wrong in the last eight years is due to Republicans inside and outside the Administration drawing some lines in the sand...
We thought transparency could help, and it does somewhat. Transparency only helps, however, if there are strongly internalized professional and social ethical commitments that are widely distributed both in the general population and among the people who do the business of government, or education, or medicine, or any other major institution. If you don’t have enough people like Grant Woods, the liberal state will fail.