A new study found that support for President Obama and the Democrats has decreased among some important voting groups. These groups helped them win two years ago. They include women, independent voters and less wealthy Americans. CBS News and The New York Times newspaper reported their findings.

Experts say the public’s poor opinion of the national economy, including high unemployment, is the main problem facing Democrats this year.

Democrats have been seeking to increase voters’ attention on individual Republican candidates they say are too extreme. Some of these candidates are supported by the conservative and libertarian Tea Party movement.

This year, money in the form of campaign contributions appears to be having more of an influence than ever before. A Supreme Court ruling opened the way for more campaign spending on television advertising by businesses and labor unions. Many television advertisements are paid for by groups not connected with political parties and by wealthy donors who do not have to identify themselves. Many of these television commercials attack a candidate’s opponent.

The election campaigns have been some of the costliest ever. For example, Republican Meg Whitman has spent more than one hundred forty million dollars of her own money on her campaign. She is seeking to become governor of California against the state’s former governor, Jerry Brown. Independent groups estimate that candidates, parties and independent groups will spend as much as four billion dollars by the time the voting has ended.