We’ve hit this ground before, but now we can see what you think! Cast your vote for the biggest reason Saxby Chambliss added 12 points to his margin over Jim Martin in just 28 days, and keep checking back for the results.

Michael Barone has his analysis — and as always, it’s a must read:

The bottom line: The Obama campaign did a magnificent job of turning out black voters in rural and small-town counties in Virginia, North Carolina, and Georgia for the November 4 election. But it was not able to replicate those results in the Georgia runoff. Black turnout pretty much matched white turnout in the inner Atlanta area, where black political organizations have been active for many years, but it failed to do so in the outer suburbs with increasing black majorities and in North Georgia counties with few blacks. Black turnout did match statewide levels in black-majority cities in southern Georgia, but not enough to outweigh similar white turnout in adjacent suburban counties. As the analysts at NBC News suggest, Obama coattails that were helpful to many newly elected Democrats in the South in November 2008 may not be so helpful to them in 2010 and any special elections that occur between now and then.

That suggests another hypothesis: that the Obama turnout effort among blacks may not be replicable. You can only vote to elect the first black president once.

In contrast, Republicans were able to produce good turnout in affluent suburban Atlanta counties, both those with few blacks and those with growing black populations. This is a countertrend to Obama’s good showings in affluent suburban counties in November—showings often far better than any previous Democrat has done since 1964. This occurred even despite Obama’s relatively moderate choices for top economic policy positions and his hints that he won’t seek tax increases on high earners anytime soon. To be sure, you won’t find any suburban counties outside the South that are as heavily Republican as some of the metro Atlanta counties. Forsyth and Cherokee counties voted more than 80 percent for Chambliss. I’m not aware of any suburban counties outside the South that vote 80 percent Republican, and even in 2004 George W. Bush did not win more than 80 percent of the vote in any congressional district in the nation. But the results here do suggest that other Democrats will have a hard time duplicating Obama’s percentages in affluent suburban counties. Note that this runoff took place when opinion is very favorable to Obama and when he has been getting credit for bipartisan or at least nonpartisan appointments (Robert Gates, Timothy Geithner).

In other words, in two years, Obama won’t be getting this kind of honeymoon feeling, and he can expect even tougher races if the Republicans can turn out the vote like this.

Mary Katharine Ham has a good roundup of reactions as well.