Retirements always pose a threat to congressional majorities. Before he took the helm of the Senate Democratic campaign committee in 2005, Sen. Charles SchumerCharles (Chuck) Ellis SchumerOvernight Health Care: Schumer calls for tying ObamaCare fix to children's health insurance | Puerto Rico's water woes worsen | Dems plead for nursing home residents' right to sue Crying on TV doesn't qualify Kimmel to set nation's gun agenda Trump knocks ‘fake’ news coverage of his trip to Puerto Rico MORE (D-N.Y.) told then-Minority Leader Harry ReidHarry ReidChris Murphy’s profile rises with gun tragedies Republicans are headed for a disappointing end to their year in power Obama's HHS secretary could testify in Menendez trial MORE (D-Nev.), "We can't let red-state Democrats retire — in '04 we lost every race where they did."

Reid agreed; Schumer subsequently won back the majority in the 2006 cycle and later helped boost the Democratic majority to 60 seats.

The Schumer-Reid exchange was detailed in Schumer's book titled, "Positively American: Winning Back the Middle-Class Majority One Family at a Time."

The Democrats who are retiring do not all hail from red states. Sen.Kent Conrad (D-N.D.) does, and Republicans are heavily favored to pick up that seat.

Republicans are also favored to win Sen. Jim Webb's (D) seat in Virginia, and their chances increase if former Virginia Gov. Tim KaineTimothy Michael KaineAuthorizing military force is necessary, but insufficient Week ahead: Crunch time for defense bill’s cyber reforms | Equifax under scrutiny Insurer Anthem to cover bare ObamaCare counties in Virginia MORE (D) opts not to run.

Sen. Joe Lieberman (I-Conn.) is also not running for reelection. Democrats are confident they can win in this blue state, especially in a presidential election year. But in all likelihood, they will have to fight for it.

Both parties will aggressively vie for Bingaman's seat. Obama won the purple state in 2008 and George W. Bush triumphed there in 2004.

Ross K. Baker, a political scientist at Rutgers University, said, "Parties in Congress, like armies in the field, suffer casualties in two ways: They are lost in election battles and they are pulled out of the line from combat fatigue after the elections are over. The Democrats have sustained both forms of loss. The combat fatigue casualties have sized up the bloody conflicts ahead on the budget, debt extension, and entitlements and have requested to be evacuated to the rear area."

He added, "This is an ominous sign for the slender Democratic majority that can berescued only with a smashing victory at the presidential level. Obama has shown he can provide coattails and he may have to do so again."

Democrats got some good news this week when Senate Minority Whip Jon Kyl (R-Ariz.) announced he would not run for a fourth term. But on Friday, Homeland Security Secretary Janet Napolitano, a former governor of Arizona, ruled out a bid.

While the retirements of the three Democrats and Lieberman have attracted many headlines and boosted the GOP's confidence, the early announcements give Democrats ample time to find strong candidates.

Sen. Patty MurrayPatricia (Patty) Lynn MurrayChildren’s health-care bill faces new obstacles Overnight Health Care: Schumer calls for tying ObamaCare fix to children's health insurance | Puerto Rico's water woes worsen | Dems plead for nursing home residents' right to sue Schumer calls for attaching ObamaCare fix to children's health insurance MORE (Wash.), who heads the Democratic Senatorial Campaign Committee, has been pushing Democratic senators up for reelection in 2012 to make up their minds early in the cycle.

Republicans picked up seven seats in the 2010 cycle, including Sen. Scott Brown's (R-Mass.) win in January last year.

Democrats are targeting Brown, who faces another tough election next year. They are also targeting Sen. John Ensign (R-Nev.), whose ethics controversies pose a major obstacle to winning a third term. Republican operatives note that Brown has a $7.2 million campaign war chest and Ensign will likely face a primary challenge.

Democratic incumbents who face reelection next year include Jon TesterJonathan (Jon) TesterOvernight Cybersecurity: Equifax security employee left after breach | Lawmakers float bill to reform warrantless surveillance | Intel leaders keeping collusion probe open Overnight Finance: White House requests B for disaster relief | Ex-Equifax chief grilled over stock sales | House panel approves B for border wall | Tax plan puts swing-state Republicans in tough spot Senators grill ex-Equifax CEO over stock sales MORE (Mont.), Joe ManchinJoseph (Joe) ManchinOvernight Energy: EPA aims to work more closely with industry Overnight Finance: Lawmakers grill Equifax chief over hack | Wells Fargo CEO defends bank's progress | Trump jokes Puerto Rico threw budget 'out of whack' | Mortgage tax fight tests industry clout Lawmakers try again on miners’ pension bill MORE (W.Va.), Sherrod BrownSherrod Campbell BrownDems plan to make gun control an issue in Nevada Mandel leads GOP primary for Ohio Senate seat: internal poll Red-state Dems need more from Trump before tax embrace MORE (Ohio), Ben Nelson (Neb.), Bill NelsonClarence (Bill) William NelsonSenate panel approves bill to speed up driverless cars Dems plan to make gun control an issue in Nevada Overnight Cybersecurity: Trump proclaims 'Cybersecurity Awareness Month' | Equifax missed chance to patch security flaw | Lawmakers await ex-CEO's testimony | SEC hack exposed personal data MORE (Fla.), Debbie StabenowDeborah (Debbie) Ann StabenowDems plan to make gun control an issue in Nevada Red-state Dems need more from Trump before tax embrace Stabenow: ‘Kid Rock might actually win the Republican primary’ MORE (Mich.) and Claire McCaskillClaire Conner McCaskillKoch-backed group targets red-state Dems on tax reform Overnight Cybersecurity: Equifax security employee left after breach | Lawmakers float bill to reform warrantless surveillance | Intel leaders keeping collusion probe open Las Vegas highlights Islamist terrorism is not America's greatest domestic threat MORE (Mo.).

Republicans need to win a net of at least three seats to control the Senate (four if Obama wins reelection).


This article was updated at 2:58 p.m.