The same day that Rasmussen shows Republicans leading Democrats by just three points on the generic ballot question among likely voters, Gallup's "first estimates among likely voters" in 2010 show the GOP up by double digits:
The numbers are pretty bad for Democrats, but two caveats:
One: Note that the Democrats do 5 points better with a higher turnout--a helpful data point that the Democrats may effectively turn into a talking point to persuade some members of their base to turn out on Election Day.
Two: "Gallup's historical election trends suggest that the race often tightens in the final month of the campaign."
In September and October 1994, 2002, and 2006, Gallup's likely voter estimates showed larger margins for the leading party than what the final estimate showed (with the final poll in 2002 moving from a slight Democratic advantage to a Republican lead in the final poll). At this point, four weeks remain until Election Day, and given the already-high levels of Republican enthusiasm, it is possible that Democrats could have relatively greater gains among likely voters over the next month. This history suggests that the likely voter model results at this point should be viewed as describing the current state of affairs, but not as predictive of the final party vote shares on Nov. 2.