Gallup tracking of 2010 congressional voting preferences shows Republicans moving back ahead of Democrats, 49% to 43%, by two points their largest lead of the campaign to date. Registered voters' preferences had been closely divided for the last several weeks.
These results are based on Gallup Daily tracking interviews conducted May 24-30. Republicans' largest advantage on the generic ballot prior to now was four points during the week of April 5-11. The GOP held a three-point advantage the week of April 12-18.
The shift from a more competitive race to a Republican lead occurred the same week President Barack Obama averaged a 46% job approval rating, his lowest weekly average to date.
Two structural changes in the data help explain the shift. First, while the percentage of registered voters identifying as Republicans has been consistent over the past several weeks, during the last week there was a decline in the percentage of voters identifying as Democrats and an increase in independent identifiers.
While the preferences of Republican and Democratic registered voters have largely been stable in recent weeks, the now-larger group of independent registered voters has shifted more toward Republicans in its voting preferences. (See more at Gallup)