A string of political setbacks has damaged Republicans' hopes of regaining the Senate majority next year and increased the likelihood Democrats might expand their razor-thin margin.

The 2008 campaign appears increasingly unpleasant for Republicans a year after unexpected defeats cost them control. Among the factors are GOP retirements in toss-up states, voters' distress over the Iraq war and a handful of scandals.

The latest blow comes from Nebraska Sen. Chuck Hagel, who was set to announce Monday that he would not seek a third term. He would have been favored heavily to win again. Democrats now hope that Bob Kerrey, a former governor and senator, will run and claim the seat.

Just recently, Sen. John Warner, R-Va., said he would give up his seat, which Democrats now considerable winnable.

Republicans once had higher hopes of reversing their 2006 setbacks, when they lost virtually every close contest and saw their 55-45 majority disappear. Now it is Democrats who feel energized, hoping to pad their majority that is essentially 51-49, when the voting patterns of two independent senators are considered.

Ethics have hurt the GOP's image — sex-related scandals involving Sens. Larry Craig of Idaho and David Vitter of Louisiana, a federal raid of Sen. Ted Stevens' Alaska home in a bribery investigation. Also, the Senate ethics committee is looking into claims that Sen. Pete Domenici, R-N.M., tried to pressure a federal prosecutor in an election probe of Democrats.

Of those, only Vitter's seat is not up for re-election. Even if Democratic victories are unlikely in the Republican strongholds of Alaska and Idaho, the scandals are a distraction that could drain money and energy the party would prefer to focus elsewhere.

Meanwhile, anti-war sentiment is giving Democrats serious hopes of denying re-election to Republican senators in competitive states including New Hampshire, Maine, Minnesota and Oregon.

Democrats "have reason to feel good," acknowledged Sen. John Ensign, R-Nev., who heads the GOP's Senate campaign committee. But, he said in an interview, Republican candidates will perform better than many people expect.

Republicans note that Democratic senators are seeking re-election in contested states such as Louisiana, Montana, Arkansas, South Dakota and Iowa. But Republicans have recruited poorly in some of those states, and Sen. Mary Landrieu, D-La., is the only incumbent that Ensign named as a potential election victim.

Democrats note that Landrieu disproved similar talk in 1996 and 2002.

The congressional elections are 14 months away, presidential campaigns will overshadow them and much can change. But Democrats are smiling, for now at least.

Warner's decision against a sixth term is perhaps the biggest gift because he is enduringly popular in a state trending Democratic. Democrats want former Gov. Mark Warner to run, although he would have to drop his vice presidential hopes to do so.

Republicans have experienced potential candidates in former Virginia Gov. Jim Gilmore and Rep. Tom Davis, but neither has Mark Warner's statewide popularity.

Democrats also hope to grab GOP Senate seats being vacated in Colorado and Nebraska. Sen. Wayne Allard, R-Colo., is not seeking a third term, and Democrats feel Rep. Mark Udall is poised to claim the seat. Republicans are banking on former Rep. Bob Schaffer.

In Nebraska, Hagel's departure gives Democrats high hopes. But Agriculture Secretary Mike Johanns, a popular Republican former governor, would be formidable against even a well-known Democrat such as Kerrey, political insiders say.

Among other closely watched races:

—Early polls in New Hampshire show former Gov. Jeanne Shaheen, a Democrat, leading first-term Republican Sen. John Sununu. But Shaheen has yet to say she will run, and Republicans say it is dangerous to discount Sununu's campaign skills.

—In Minnesota, first-term GOP Sen. Norm Coleman faces a potentially tough challenge from TV comedian Al Franken or lawyer Michael Ciresi. The Iraq war seems likely to dominate the campaign.

—In Oregon, which President Bush lost twice, Republican Sen. Gordon Smith has become one of his party's sharpest critics of the war. Democrats say that will not win him a third term, but they failed to recruit their top two choices. State House Speaker Jeff Merkley is the likely nominee.

—In Maine, two-term Sen. Susan Collins, R, has proven popular with voters, but anti-war sentiment runs high. Unlike her Democratic challenger, Rep. Tom Allen, she voted in 2002 to authorize the war.

Ensign, the Republican campaign chief, predicted all four incumbents would survive.

"If you scratch the surface, things don't look necessarily that good," he said. "But when you get below the surface, things aren't nearly as bad as what they could be."

Ensign's Democratic counterpart, New York Sen. Chuck Schumer, said in an interview, "the wind is at our back."

Anything can happen in 14 months, Schumer said, but voters show a hunger for change, especially in Iraq. Generic polls on party preference find a heavy advantage for Democrats, he said, suggesting Republican senators will have trouble distancing themselves from Bush.

"We feel good," he said.