In his announcement that he wouldn't challenge Kirsten Gillibrand in New York's Senatorial primary, Manhattan Borough President Scott Stringer indicated that he made that decision mainly to fit with President Obama's wishes:
"In light of President Obama's clear desire to avoid a Democratic primary in New York state, I have decided to focus on my reelection race for Manhattan borough president and to suspend my exploratory committee and fundraising efforts for the 2010 Senate race," Stringer said.
President Obama survived one of the most bitterly contested primaries in Democratic history, which perhaps is a source of his reputed antipathy toward primaries. However, research on whether primaries help or hurt parties in general elections shows decidedly mixed results:
In researching Democratic primaries in recent House and Senate campaigns, David Kowalski and I both found a generally, though not universally, positive effect on Democratic general election performance.
As we all saw in the blogosphere in 2008, divisive primaries can have a negative effect on personal relationships and involvement in political social networks. However, as we also saw in 2008, it can be reasonably countered that while the existing participants within political social networks can fracture as a result of a divisive primary, such primaries can also bring many new people into the social networks.
There probably isn't any universal rule on whether contested primaries help or hurt, because there isn't any universal way in which contested primaries unfold, or any universal context in which they take place.
Still, there are good reasons to recoil from powerful figures within parties trying to prevent primaries. The entire exercise reeks of powerful people trying to protect other powerful people, and one the last thing we need these days are even fewer ways to hold politicians accountable. Uncontested primaries cuts the number of electoral opportunities we have to hold politicians accountable in half, and that just isn't a good thing. I know that I feel personally disenfranchised when primary fields are cleared for an establishment favorite. I'm sure that President Obama would have felt the same way if everyone in the Democratic Party had worked to clear the field for Hillary Clinton.