Retirements always pose a threat to congressional majorities. Before he took the helm of the Senate Democratic campaign committee in 2005, Sen. Charles SchumerCharles SchumerSaudis hire lobbyists amid 9/11 fight Consumer bureau remains partisan target after Wells Fargo settlement Overnight Healthcare: Planned Parenthood deal in sight in Senate | A new 'public option' push MORE (D-N.Y.) told then-Minority Leader Harry ReidHarry ReidBlack Caucus demands Flint funding from GOP Report: Intelligence officials probing Trump adviser's ties to Russia White House preps agencies for possible shutdown 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 KaineTim KaineKaine participates in Native American pow wow Sunday shows preview: Both sides gear up for debate Longtime Clinton aide Reines playing Trump in mock debates: reports 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."
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 MurrayPatty MurrayDems call for better birth control access for female troops US wins aerospace subsidies trade case over the EU Senate Dems unveil new public option push for ObamaCare 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 TesterJon TesterOvernight Healthcare: Mylan CEO to defend record on EpiPens | Medical cures bill delayed to lame duck | House GOP hopeful about Zika deal Tribes open new front in fight over pipelines Dem lawmakers: Clinton should have disclosed illness sooner MORE (Mont.), Joe ManchinJoe ManchinDemocrat vows to go after opioid makers – including daughter's company Overnight Healthcare: McConnell unveils new Zika package | Manchin defends daughter on EpiPens | Bill includes M for opioid crisis Democrat defends daughter after tough EpiPen grilling MORE (W.Va.), Sherrod BrownSherrod BrownOvernight Finance: McConnell offers 'clean' funding bill | Dems pan proposal | Flint aid, internet measure not included | More heat for Wells Fargo | New concerns on investor visas House votes to eliminate Olympic medal tax Senate Dems call for investigation into Wells Fargo's wage practices MORE (Ohio), Ben Nelson (Neb.), Bill NelsonBill NelsonGOP puts shutdown squeeze play on Dems Overnight Healthcare: McConnell unveils new Zika package | Manchin defends daughter on EpiPens | Bill includes M for opioid crisis Dem to support spending bill despite no Flint aid MORE (Fla.), Debbie StabenowDebbie StabenowGOP puts shutdown squeeze play on Dems Senate panel approves pension rescue for coal miners Week ahead: Flint aid fight shifts to House MORE (Mich.) and Claire McCaskillClaire McCaskillFacebook steps up fight against fake news The Trail 2016: Off the sick bed McCaskill: Trump and Dr. Oz a 'marriage made in heaven' 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.