Representative Jane Harman's decision to resign from Congress to take a think-tank post will give California's "top-two" primary system adopted last year via a voter referendum an early test and lots of exposure. This is a seat with a strong majority of registered democratic voters so the key question at issue is more likely to be what kind of Democrat wins the seat rather than a partisan battle. But the prospects for some interesting politics is in store. Under normal circumstances, the critical contest would be in the democrats' primary, with the winner there coasting to victory over the republican candidate in the general election. Under the new law, there will be an open primary and unless one candidate wins a majority, the top two will runoff against each other, even if they are in the same party. In this system, republicans -- who pulled 35% of the vote against Harman in 2010, have interesting choices. In round one, they can either back a republican to try and get a candidate into a runoff (where she will almost certainly lose) or get behind a conservative or moderate democrat to make sure a progressive democrat doesn't run away with the prize in the first round. Democratic candidates will have to broaden their appeal. Progressives can't just cater to their base to win the primary and then assume they will coast to victory in the general election, since they could face a moderate democrat that could put together a coalition of moderate democrats & republicans to win. Who knows what the result will be -- but at least there is the potential for some healthier politics where candidates must try to appeal to broader sections of their constituency and voters have the opportunity to cast meaningful votes throughout the process.