Gallup's most recent generic ballot poll found registered voters virtually tied in their preference for voting for a Republican ticket (45 percent) or for a Democratic one (46 percent). Last week's generic ballot went 43 percent Democratic and 48 percent Republican, and the previous week's showed another tie. For Democrats, this is an improvement from the August average of 49 percent Republican and 43 percent Democratic.

The bad news for Dems, however, is the growing enthusiasm gap. Gallup found Republicans led Democrats by 19 points in terms of voter enthusiasm:

Republicans have enjoyed at least a 10-point advantage on this measure since Gallup began tracking congressional election preferences in March, including margins of 16 points or higher since August. 

Given this continuing enthusiasm gap between Republicans and Democrats, even a tie in registered voters' preferences will almost certainly mean the Republicans will garner the most votes on Election Day. ...

Republicans have so far this month lost a little of the unprecedented strength they had among registered voters in August. Voting intentions among registered voters from Sept. 1-19 show a virtual tie between Republicans and Democrats, which is down from the six-point Republican advantage in August. Gallup will begin estimating the voting preferences of the probable 2010 electorate in October, which is highly likely to show a larger Republican advantage than is seen among registered voters.

Read the full story at Gallup.