Gallup’s latest analysis shows that Democrats have not just lost ground on the national level, but also within states as well.  Using a general-population sample (more on that in a moment), the survey shows that Democrats have gone from a twelve-point advantage on the eve of Barack Obama’s big win in 2008 to a mere four-point, within-the-MOE lead in party identification.  Fewer states are showing significant Democratic advantage as a result:

More states are politically competitive this year than was the case in 2009, as fewer Americans nationwide identify with the Democratic Party. Vermont — along with the District of Columbia — is the most Democratic state in the U.S. in 2010 so far, while Utah, Wyoming, and Idaho are the most Republican.

These results are based on interviews with more than 175,000 U.S. adults, conducted between January and June 2010 as part of Gallup Daily tracking. …

Nationwide, Democrats have a 4-point party identification advantage over Republicans in 2010 (44% to 40%), down from an 8-point advantage in 2009 and a 12-point advantage in 2008.

While Democrats’ party strength fell in each of the last two years, Republicans have not gained concomitantly. Instead, the percentage of Americans who do not identify with or lean toward either political party has increased.

The sample is the key.  Gallup did not ask for registered or likely voters, but instead opted for the wider but less accurate sampling technique.  We have a basis of comparison as well, the 2008 election.  Gallup showed Democrats with a 12-point advantage in the general population, but Obama only won the popular vote by seven points — and that was with the help of Republican crossovers.  The general-population sample overstates Democratic support in actual elections, even the one with massive turnout that propelled Obama into the White House.

The four-point advantage today, therefore, looks pretty thin.  Among registered voters, it’s probably dead even or perhaps a negative number.

The sample didn’t help Democrats with the states.  Two years ago, Democrats had significant advantage in 30 states.  In 2009, that number dropped to 24.  This year, it’s 14.  A few of those states went into the “leaner” category for Democrats, going from 6 to 10 and then to 9, respectively.  Overall. the number of states with Democratic advantage has dropped from 36 to 23 in just two years.  Republican states have grown from 5 to 12 in the same period, with the rest too close to call.

Gallup concludes that Republicans will have a good midterm in Congressional seats, but that’s more or less known already.  The bigger problem for Democrats will be in the state houses.  Redistricting starts next year, after the 2010 Census reports get published.  If Republicans take control of more state houses, they may drive more of the redistricting — and that has implications well beyond these midterm elections.