The Democrats' shrinking margin of support "suggests the 2010 election could be quite close if it were held today given low turnout in midterm elections and the usual Republican advantages in turnout," Gallup said.
"Thus, at this early stage, 2010 does not look like it is shaping up to be as strong a Democratic year as 2006 was, and that could make it difficult for the party to hold onto the gains it made in the 2006 midterm and 2008 presidential elections," the respected polling service said.
Nowhere, perhaps, is the nation's political shift more evident than in the Senate races, where stronger Republican recruiting has raised prospects in a number of heavily Democratic states, some of which have not been on the GOP's radar screen until now. Among them:
-- Connecticut: Five-term Sen. Christopher Dodd, badly weakened by charges he received low-interest mortgage loans from a Countrywide pal, is trailing or tied with two of his potential Republican challengers.
-- Illinois: Republican odds of filling Obama's former Senate seat improved significantly when popular state Attorney General Lisa Madigan turned down White House pleas to run. Republicans are fielding their strongest candidate, Rep. Mark Kirk, who has strong crossover appeal to Democrats. The race is now considered a tossup.
-- California: Former Hewlett-Packard CEO Carly Fiorina is trailing three-term liberal Democrat Sen. Barbara Boxer by a mere four points in the latest Rasmussen poll.
-- Pennsylvania: When Sen. Arlen Specter switched parties, he won endorsements from all the top Democrats, including Obama and Gov. Ed Rendell, amid forecasts he would put the seat in Democratic hands. But Democrats have since cooled to his candidacy, and he faces a primary challenge. A Quinnipiac University poll now shows him in a dead heat with former Rep. Pat Toomey, the expected GOP nominee.
But the 2010 election climate will largely be shaped by the way voters rate Barack Obama's performance as president. A recent Rasmussen daily tracking poll found that the nation's voters strongly disapproved of Obama's performance by 40 percent to 28 percent.
Unless Obama's approval numbers turn around in the second half of this year, Democrats will enter the midterm-election season at a disadvantage when, historically, the party out of power makes gains in Congress.
Republicans intend to turn the 2010 election into a national referendum on his presidency, and the evidence thus far suggests the GOP will likely make significant political gains at his expense.