Republicans have taken the largest lead in the 2010 Congressional election cycle in a generic poll that tests would-be voters' party loyalties.

Gallup's poll has shown the two parties neck and neck in recent days. But in a release today, the polling agency said they saw "Republicans moving back ahead of Democrats, 49% to 43%, by two points their largest lead of the campaign to date."

"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," Gallup noted.

Obama's -- and by extension Democrats' -- approval ratings may be sliding in the wake of a giant oil spill in the Gulf of Mexico. Critics, including some from his own party, have argued that Obama was slow to respond and should have taken over handling containment from oil giant BP.

Notes Yahoo News' Holly Bailey:

According to Gallup, the GOP gained 3 percentage points in the poll over the last week, while Dems fell 4 points. All of this happened as President Obama's approval rating took a hit, especially with his handling of the Gulf of Mexico oil spill. Gallup puts Obama's approval rating at 46 percent — not exactly in George W. Bush territory, but low for this White House.

No doubt critics will question how much a generic poll really reveals about what might happen in November...

One number that Democrats are surely not pleased about is what poll experts call the "enthusiasm" gap. According to Gallup, 39 percent of Republicans are excited about the 2010 elections, compared with just 24 percent of Democrats. That's one of the leading measures of how likely it is that voters will turn out to vote, and if Democrats can't find a way to close that 15-point gap, November could be a painful month for President Obama and other party leaders.