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 SchumerCan Mueller be more honest than his colleagues? Throwing some cold water on all of the Korean summit optimism House Republicans push Mulvaney, Trump to rescind Gateway funds MORE (D-N.Y.) told then-Minority Leader Harry ReidHarry Mason ReidGOP moves to cut debate time for Trump nominees Harry Reid: ‘The less we talk about impeachment, the better off we are’ Lobbying world 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 KaineOvernight Defense: VA nominee on the ropes | White House signals it will fight for pick | Trump talks Syria with Macron | McConnell tees up Pompeo vote House lawmakers renew push for war authorization We need more congressional oversight on matters of war 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 MurrayOvernight Health Care: Trump's VA pick on the ropes | White House signals it will fight for nominee | Senate panel approves opioid bill | FDA cracking down on e-cig sales to kids Trump's nominee for the VA is on the ropes Senate Health panel approves opioid bill 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) TesterThe Memo: Jackson ‘fiasco’ casts pall on White House Republicans want Trump’s VA nominee to withdraw Overnight Health Care: New allegations against VA nominee | Dems worry House moving too fast on opioid bills | HHS chief back in DC | FDA reexamines safety of controversial Parkinson's drug MORE (Mont.), Joe ManchinJoseph (Joe) ManchinMcConnell hits back at 'ridiculous' Chinaperson remark Overnight Defense: New allegations against VA nominee | Pompeo vote set for Thursday | Work begins on defense policy bill | Measures push space corps, pay bump for troops Pompeo set to be confirmed on Thursday MORE (W.Va.), Sherrod BrownSherrod Campbell BrownOvernight Finance: Mulvaney remark on lobbyists stuns Washington | Macron takes swipe at Trump tariffs | Conservatives eye tax cut on capital gains | Gillibrand unveils post office banking bill | GOP chairman pushes banks on gun policies Top banking Dem calls for Mulvaney to resign after lobbyist remarks Senator offers new details on allegations against VA nominee MORE (Ohio), Ben Nelson (Neb.), Bill NelsonClarence (Bill) William NelsonTucker Carlson criticizes GOP for campaigning against Clinton: She ‘doesn’t run anything’ Senators debate new business deduction, debt in tax law hearing Winners and losers from Jim Bridenstine’s confirmation as NASA administrator MORE (Fla.), Debbie StabenowDeborah (Debbie) Ann StabenowVulnerable Senate Dems have big cash advantages Senators push HHS to negotiate lower prices on opioid overdose reversal drug Senators press administration on mental health parity MORE (Mich.) and Claire McCaskillClaire Conner McCaskillOvernight Cybersecurity: DHS cyber nominee vows to make election security 'top priority' | CIA to allow lawmakers to review classified info on Haspel | Dems raise security concerns about Trump's phone use Election security dominates hearing for Trump Homeland Security nominee Overnight Cybersecurity: Homeland Security official says Russia likely targeted more than 21 states | Senate approves Trump's NSA chief | Lawmakers unveil bipartisan internet privacy bill 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.