Barack Obama has held a minute lead in most head-to-head polls since it became clear that he and John McCain would be the presidential contenders, Obama and Biden enjoyed a surge after the Democratic convention, and now it appears that the pendulum is swinging back.The news that has many progressive hands wringing today, via USA Today and Gallup:The Republican National Convention has given John McCain and his party a significant boost, a USA TODAY/Gallup Poll taken over the weekend shows, as running mate Sarah Palin helps close an "enthusiasm gap" that has dogged the GOP all year. McCain leads Democrat Barack Obama by 50%-46% among registered voters, the Republican's biggest advantage since January and a turnaround from the USA TODAY poll taken just before the convention opened in St. Paul. Then, he lagged by 7 percentage points. The convention bounce has helped not only McCain but also attitudes toward Republican congressional candidates and the GOP in general.How fickle the electorate must appear when viewed in this context:Looking a bit deeper, there are a few things to point out.First, the Gallup numbers -- both its daily tracking poll with McCain up by 5 among registered voters and the Gallup/USA Today poll of likely voters, with McCain suddenly up by 10 -- are outliers, and without Gallup's results, the rolling average remains basically a statistical dead-heat. CNN, Rasmussen and the Hotline/ Diageo polls all show essentially a tied race.I should also note that Gallup's "likely voter" model has a partisan breakdown as follows:Republican -34 percentDemocrat -33 percentIndependent - 32 percentThat's suspect; the Dems have enjoyed a partisan advantage for some time. According to Rasmussen, the most recent to poll it, the Dems' advantage has shrunk over the last month but still stands at close to six points:During August, the number of Americans who consider themselves to be Republicans increased two percentage points to 33.2% while the number of Democrats was little changed at 38.9%.