But energizing Democratic voters could be a major challenge this year. The public has a negative view of the economy, and that is reflected in weakening approval ratings for President Obama.

In addition, conservative and libertarian activists under the banner of the Tea Party movement are energized this year, urging voters to make a statement against the president's economic policies and against the Democratic majority in Congress.

John Fortier is a political analyst at the American Enterprise Institute here in Washington.

"In general, I think the atmosphere is greatly improved for Republicans by the Tea Party," said Fortier. "A focus on economics and small government is good for the Republican Party. And the voters who will come out to support their candidates will generally bring them to victory."

Democrats are spending a lot of time trying to motivate younger voters this year because, historically, they have been less likely to vote in congressional midterm elections than older voters.

This year, that could be a serious problem for Democrats, says pollster Celinda Lake.

"Younger voters are the most Democratic voters," said Lake. "Seniors remain the toughest for us. And if there is a story line in this election that is slightly different than the past, it is the animosity of seniors who will show up to vote."

The Tea Party movement is popular with many older voters who are upset about the size of government and who want to cut taxes and government spending.