While U.S. President Barack Obama has spent weeks campaigning countrywide for Democrats in the run-up to the Congressional elections, his speeches and "backyard chats" have done little to change forecasts of big Republican gains for November.

That is because voters' major concern is jobs as unemployment rates linger near double digits, and recent polls show that Americans give the president poor marks on his handling of the economy.

Still, some analysts say Obama could help Democrats somewhat if he tries to get young people and African Americans out to vote.

"Obama's travels and public rallies are not likely to change the election dynamic or the overall Republican or Democratic enthusiasm to vote," said John Fortier, a fellow at the American Enterprise Institute.

The approval rating of Obama has plunged from around 70 percent at the start of his presidency to less than 50 percent now.

That is setting GOP candidates up for big wins in November -- some Democratic candidates even tried to distance themselves from the president, focusing on issues important to their districts.

Blaming Bush is not helping

The president's main theme has been to urge voters not to return to the Republican policies that he argues got the United States into the economic mess it is in today.

At a fundraiser in Miami on Monday, Obama referred to the GOP Pledge to America -- the party's main election platform -- as "snake oil."

"Do we return to the same failed policies that ran our economy into a ditch, or do we keep moving forward with policies that are slowly pulling us out?" he said last month in Ohio.

That message, however, is not resonating with many voters, as Americans are increasingly viewing the Great Recession as belonging to Obama.

Dan Mahaffee, special assistant to the president at the Center for the Study of the Presidency and Congress, said voters tend to have very short memories. And after 18 months, they are no longer linking the worst recession since the 1930s to the previous administration.