If people thought the enthusiasm had leaked out of the Republican resurgence in midterm polling — people like Gallup, for instance — they need to think again.  And to Gallup’s credit, they have at least polled again, and found that the GOP has leaped to its largest lead in the generic Congressional ballot this year.  In fact, Republicans have opened a double-digit lead among independents in this survey of registered voters:

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. …

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.

The partisan gap has narrowed significantly in the last week, although this is probably an issue with sampling in the previous survey than a particular trend.  The May 23rd survey showed a 5-point gap between Democrats and Republicans, with independents 11 points back.  This week has the three in a virtual tie, with 33% of respondents identifying as Democrats and 32% each for Republicans and independents.  Partisan splits in surveys designed to accurately measure them rarely show independents so far behind the two major parties and usually put them at least in parity.

The change in the sample could account for the bump seen in the polling, but that doesn’t account for the change in independent preference.  At the beginning of May, independent voters leaned Republican by six points, 44/38.  Over the last four weeks, that advantage has grown to thirteen points, 47/34, even as the pool of independents has grown in the survey.  That’s a bad sign for Democrats heading into primary season in many states, and a welcome trend for Republicans.

As far as enthusiasm goes, the end of the ObamaCare debate did take the wind out of the sails of Republicans … but also Democrats and independents.  Republican voters still have a lead of 15 points on enthusiasm over Democrats (39/24), down from 54/35 at the beginning of April.  Independents edge Democrats on enthusiasm at 25%, down from a peak of 36% in March and mid-April.  The last three surveys on enthusiasm all have Democrats trailing independents on enthusiasm, and given the big lead Republicans have in that group, it’s yet another bad sign for Democrats in the midterms.