With all the controversy swirling around embattled San Francisco Supervisor Ed Jew regarding FBI investigations and his in-district residency, some have asked the question: How did this guy ever get elected?

Ironically the answer reveals a new dynamic in San Francisco elections that may diminish the nastiness of mudslinging campaigns, to the relief of all. San Francisco has seen its share of vicious political races. Campaign mailers showing Nazi swastikas, cockroaches and pornography, along with accusations of anti-Semitism, slum landlordism and more, have defiled our mailboxes and doorsteps. While negative campaigning will never go away, it may be possible to decrease the most gratuitous forms of mudslinging. How? That's where understanding how Ed Jew got elected comes in.

Certainly, part of the answer is he knocked on a lot of doors and built support in his community. But a key factor also appears to be that he didn't campaign negatively, and his opponents did. And due to the ranked choice voting system used to elect San Francisco's local offices, his opponents' mudslinging backfired. An exit poll study from Jew's District 4 race in 2006 commissioned by the Asian Law Caucus reveals some interesting results that bear on this question. One of the conclusions from that exit poll stated: "Negative campaigning drives (Jaynry) Mak and (Doug) Chan supporters to vote overwhelmingly for Jew as second choice."

Mak and Chan were considered two front-runners because they had endorsements from the city's bigwigs and the most money. But they began attacking each other, in the process alienating each other's supporters. This created a dynamic where Mak and Chan supporters ranked Jew as their second choice. When their first choice was eliminated from the "instant runoff," their vote went to Jew, making him the top choice among Asian voters, and ultimately all voters. One of the things that has been said about "instant runoff," also known as ranked choice voting, is that it creates incentives for candidates to find common ground and build coalitions using the ranked ballots, rather than the incentives in a traditional runoff of using mudslinging to tear down your lone opponent. The idea is that if you need the second or third rankings from the supporters of your rivals in order to win, you have to be more careful what you say about them. We saw evidence of that in the District 5 race in 2004, when 22 candidates ran for an open seat. Rather than the predicted bloodbath, campaigning was generally civil with some candidates holding joint fundraisers and others recommending a second choice to their supporters, prompting a New York Times article headlined: "New Runoff System in San Francisco Has Rival Candidates Cooperating."

So the Asian Law Caucus exit poll provides corroboration of that view. Moreover, when the two leading Asian candidates in District 4 began attacking each other, the Asian vote didn't split. Voters had other choices, having been liberated to rank more than one candidate. And this preserved a de facto coalition in the heavily Asian Sunset district because these voters could give their second ranking to the Asian candidate (Jew) who remained above the fray.

Such coalition-building shows how ranked choice empowers voters. Even though the leading Asian organizations split their endorsements among various candidates, voters were able to figure it out without any signaling from political elites. And the "open primary" format allowed voters to use their rankings to avoid the straitjacket of restricted choices usually caused by a traditional runoff election, as well as the terrible mudslinging that often occurs.

This underreported dynamic offers to voters a bit of relief from the incessant backstabbing of politics and what has been called fittingly the "politics of personal resentment." This doesn't mean that candidates all will be bland softies who never criticize each other. Quite the contrary, it means when they do disagree it will be more from a point of principle, based on the issues, rather than "Swift boat" muggings based on malicious distortions.

Campaign debate will be informative. But ranked choice only will lead to less viciousness if more San Francisco candidates and political consultants understand this dynamic. Indeed, both Mak and Chan hired high-priced campaign consultants who are known for their attack-dog style politics. Yet in the District 4 race it backfired.

Political cultures often are resistant to change, but as more candidates lose due to gratuitous mudslinging, and more candidates win by building coalitions and attracting second and third rankings, we may discover the format contributes to a decrease in the politics of personal resentment -- even in San Francisco.

Steven Hill is director of the political reform program of the New America Foundation and author of "10 Steps to Repair American Democracy."