For Republicans, it is pretty hard to avoid an optimistic outlook about the fall elections.

While incumbents elected to Congress have considerable advantages (for example, greater name recognition and better funding), they are also susceptible to periodic “wave” elections, where fed up voters reject members of one party across the board. Democrats were the victim of a “wave” in the 1994 elections and Republicans in 2006. Right now, it seems that Democrats may be swept away in 2010.

In the House of Representatives, where Democrats have about a 255-178 majority (there are a few vacancies), Republicans now seem likely to make major gains and have a very significant possibility of actually gaining the controlling the chamber, and replacing Nancy Pelosi as speaker.

A number of polls collected at the Real Clear Politics website give the GOP an actual advantage in the generic ballot (voters are asked if they would prefer a Democratic or Republican to represent them in the House), which is fairly unusual. Some red state House Democrats facing tough reelection campaigns, such as two members in Tennessee and one in Kansas, have decided not to run and one Democratic member in Alabama switched parties. This week Democratic Rep. Patrick Kennedy of Rhode Island decided not to seek reelection, although personal factors may have played a part. Even in New York State, Republicans at a minimum have a strong shot at picking up three seats, one on Staten Island and two upstate seats where Democrats won special elections.

In the Senate, things look good for Republicans as well, although winning the ten seats needed for control remains a longshot. Obviously, the party was very much buoyed by the upset victory in Massachusetts of Scott Brown. Looking forward, there are numerous strong possibilities for gains. In addition to an almost certain pickup in North Dakota, the GOP has a strong shot in Nevada to oust majority leader Harry Reid, and also a good shot to win Vice President Biden’s old seat in Delaware and are very much in the running to capture President Obama’s former seat in Illinois. Even New York Democratic Senator Kirstin Gillibrand is not completely out of the woods.

The bombshell Senate retirement of this week is in Indiana, where Senator Evan Bayh decided not to seek reelection, complaining of excessive partisanship in the chamber. Senator Bayh, himself the son of a former Indiana senator, was a former governor of the state and had won two terms in the Senate. He is just 54 years old, had a substantial campaign warchest, and was generally considered a favorite to be reelected. Mr. Bayh’s departure was labeled a “game changer” by Republicans, who promised to field a top tier candidate. The race for the seat was immediately switched by Cook Political Report from “leans Democratic” to “leans Republican”).

Can the Democrats avoid disaster? Clearly they will be helped if the economy recovers significantly in 2010, although signals are very mixed, especially concerning employment.

The biggest question is whether Mr. Obama and the Democratic leadership should move to the center on issues like health care and energy. While the base of the party favors soldiering on with existing proposals and perhaps being able to show voters in November concrete legislative successes, that strategy could prove self-defeating. Many independents and conservative Democrats may feel that they did not vote for a sweeping left wing agenda when they pulled the level for Mr. Obama in 2008 and that voting Republican is the best hope to restore political balance.