Vermont Gov. Peter Shumlin, a third-term Democratic governor who has grown increasingly unpopular in his home state, will not seek reelection in 2016.

At a press conference Monday, Shumlin said he based his decision on the belief that governors should serve no more than three two-year terms, as well as on his conviction that he will have achieved much of what he set out to accomplish when he was first elected by the time his current term expires in 2017.

Shumlin's management of the state's health exchange contributed to his unpopularity, as did his postelection decision to scrap plans to establish a single-payer system in the state. Shumlin thanked his staff and touted his accomplishments in his Monday announcement, but cited his failure to achieve single-payer as a standout exception.

Shumlin's unexpectedly tough reelection contest in 2014 drew his political future into question. Shumlin barely beat a total political unknown, Republican businessman Scott Milne, by less than a percentage point, and failed to win the 50 percent necessary to declare victory. The result was ultimately decided by the legislature. The embarrassment was compounded by his role at the time as chair of the Democratic Governors Association. After the near-loss, his unpopularity was evident. A poll released in March from the Castleton Polling Institute showed him with an approval rating of just 41 percent, with 47 percent disapproving.

"In the weeks following another successful legislative session, I had a chance to reflect on the progress that we've made since taking office," Shumlin said Monday. "As I consider the path that we're on, and I look ahead to the critical work we still have over the next 18 months, I believe that we will have accomplished, and in many ways, in many cases exceeded my expectations of the work we set out to do when I became governor. I am announcing today for those reasons that I will not be a candidate for a fourth term in 2016."

Now, Democrats face a puzzling prospect: Even in deep-blue Vermont—the state that repeatedly picks socialist Bernie Sanders as its senator—they may lose the governor's mansion to a Republican.

Before Shumlin announced his decision Monday, Republicans were pinning their hopes on their only statewide elected official: Lt. Gov. Phil Scott, who is exceptionally popular and widely considered capable of running competitively for higher office. Scott told local TV station WCAX last week that he was considering running for governor in 2016, and said "I think my decision won't have any bearing on whether [Shumlin] runs or not."

Shumlin was so weak that he also faced the threat of a potentially contested Democratic primary, and the possibility of an independent challenge from a Progressive Party candidate. Democratic state House Speaker Shap Smith and former state Sen. Matt Dunne expressed varying degrees of interest in seeking statewide office next year, and did not rule out gubernatorial bids. Smith said he would not run against Shumlin in a primary. Dunne expressed interest regardless of what Shumlin's plans were.

Former Shumlin adviser Bill Lofy said without Shumlin in the race, he expects Rep. Peter Welch to face heavy pressure from Democrats to run. "Congressman Welch would be the prohibitive favorite. He has a proven record of representing Vermont successfully in Congress and I think would cause any other potential candidate for governor to take pause before jumping into a race," Lofy said.

Welch, however, is far from certain to jump into the race: "It's likely Congressman Welch will seek reelection to Congress, but this news comes as a surprise, so he will be taking the time he needs to thoughtfully consider how he can best serve Vermonters," said Welch chief of staff Bob Rogan.

One Vermont Democratic political operative described a potential contest between Scott and Welch as a "battle royale" of the variety most don't expect from the solidly blue state.

Shumlin said Monday that he will "fight to ensure that whoever takes my place as governor is a Democrat."

One source at the Republican Governors Association told National Journal that the group was planning on committing serious resources to the race in 2016 had Shumlin run, but in an open race the money spent there will depend on who the Democratic nominee is and the strength of their candidacy, since Shumlin was viewed as uniquely vulnerable.

RGA communications director Jon Thompson said the group views Vermont as a "strong pickup opportunity for Republicans in 2016" with or without Shumlin in the race. He acknowledged that "winning Vermont in a presidential year will always be an uphill climb for Republicans, but we are confident that a Republican candidate with a positive vision for the state can put together a winning coalition."

Outside of Scott, Republicans have a thin bench, but the fact that the party is hoping to contest the 2016 race reflects the extent to which Republicans have proven capable of extending their reach into the states. Republicans control 31 governorships and are eyeing more.

Since Scott first won election in 2010, he's gained a reputation as an earnest, down-to-earth political moderate who cares deeply about the state and has forged good relationships with members of both parties. One thing Scott's best known for is his affinity for stock-car racing. He's been competing at the Thunder Road International SpeedBowl in Barre since 1992. Scott won reelection in 2014 with 62 percent of the vote while Shumlin floundered.

In years past, Scott said he would only seriously consider running for governor "if all the stars aligned for me personally and for Vermont as a whole." Shumlin's vulnerability appeared to present that ideal situation. An open race would be a tougher situation for Scott.

Even Democrats are quick to offer praise for Scott. "Phil is a great guy. He's authentic, and he loves Vermont and wants what's best for Vermont," Lofy said. "The challenge that Phil Scott has is, it's unclear what he really stands for, and it's not clear that he really wants to be governor of Vermont. Running in a contested race for governor in an open seat, in a presidential year, for a Republican is a very steep hill to climb."

Shumlin said he plans to return to his private business after his term expires in 2017, and said he has no desire to run for federal office or live in Washington.

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