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 SchumerTrump goes after Democrats over photo of drowned migrants Schumer displays photo of drowned migrants on Senate floor in appeal to Trump McConnell-backed Super PAC says nominating Roy Moore would be 'gift wrapping' seat to Dems MORE (D-N.Y.) told then-Minority Leader Harry ReidHarry Mason ReidSenators briefed on US Navy's encounters with UFOs: report Key endorsements: A who's who in early states Trump weighs in on UFOs in Stephanopoulos interview 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 (Tim) Michael Kaine2020 debates complicate Senate plans for vote on Trump's war authority Senate Health Committee advances bipartisan package to lower health costs Senate GOP to defeat proposal requiring approval for Iran attack 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 MurraySenate Health Committee advances bipartisan package to lower health costs Overnight Health Care: Trump officials defend changes to family planning program | Senators unveil bipartisan package on health costs | Democrats pass T spending bill with HHS funds Chris Murphy may oppose bipartisan health bill unless it addresses ObamaCare 'sabotage' 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) TesterDemocrats leery of Sanders plan to cancel student loan debt VA chief pressed on efforts to prevent veteran suicides Overnight Defense: US to send 1K more troops to Mideast amid Iran tensions | Iran threatens to break limit on uranium production in 10 days | US accuses Iran of 'nuclear blackmail' | Details on key defense bill amendments MORE (Mont.), Joe ManchinJoseph (Joe) ManchinManchin on 'Medicare for All': 'We can't even pay for Medicare for some' Overnight Energy: New EPA rule could expand officials weighing in on FOIA requests | Trump plan to strip conservation fund gets bipartisan pushback | Agriculture chief downplays climate concerns Trump plan to strip public land conservation fund gets bipartisan pushback MORE (W.Va.), Sherrod BrownSherrod Campbell BrownHouse panel to hold hearing on Facebook cryptocurrency project Democrats talk up tax credits to counter Trump law Facebook's new cryptocurrency raises red flags for critics MORE (Ohio), Ben Nelson (Neb.), Bill NelsonClarence (Bill) William NelsonDemocrats target Florida Hispanics in 2020 Poll: Six Democrats lead Trump in Florida match-ups How Jim Bridenstine recruited an old enemy to advise NASA MORE (Fla.), Debbie StabenowDeborah (Debbie) Ann Stabenow It's time to let Medicare to negotiate drug prices Trump judicial nominee says he withdrew over 'gross mischaracterizations' of record Trump judicial nominee withdraws amid Republican opposition: report MORE (Mich.) and Claire McCaskillClaire Conner McCaskillConservatives spark threat of bloody GOP primaries Congress needs to work to combat the poverty, abuse and neglect issues that children face Lobbying world 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.