In the wake of U.S. Sen. Olympia Snowe’s surprise decision not to seek another term, political observers in Maine and in Washington, D.C., were considering Wednesday what the senior senator’s departure means for Maine and for the political balance on Capitol Hill.

Snowe and her Maine colleague, Sen. Susan Collins, are just two of 100 senators. Together, however, the pair of moderate Republicans have enjoyed outsized influence in the Senate in recent years as they frequently became crucial swing votes on major issues, from President Barack Obama’s stimulus package to Wall Street reform and repeal of the military’s “Don’t Ask, Don’t Tell” policy.

Additionally, Snowe holds a prominent seat on the powerful Senate Finance Committee and is respected for her in-depth knowledge on a range of topics.

“She will be missed for a lot of reasons, not the least of which are her expertise on a lot of issues and her sort of voice of reason,” said Jennifer Duffy, editor and political analyst on Senate issues for The Cook Political Report, one of the most influential inside-the-Beltway sources on campaigns and politics. “She has a lot of influence as a swing vote.”

So how does Snowe’s departure next winter affect her constituents back home?

“Seniority is everything, so when a state — and especially a small state — loses somebody like Snowe with so much seniority, it is felt,” Duffy said. “The good news is Collins is still there and Collins has a lot of influence. But it is a heck of a lot easier when you have two senators.”

Snowe has represented Maine in Congress for 33 years and faced relatively few serious challengers during that time. She became the youngest Republican woman in U.S. history to be elected to the U.S. House of Representatives in 1978 and the first woman to serve in both chambers of Congress and a state legislature with her election to the Senate in 1994. She is married to former Maine Gov. John McKernan.

Those political accomplishments were despite a life marred by tragedy, including the death of both parents while she was young and becoming a widow at age 26 after the sudden death from a car accident of her first husband, Peter Snowe.

A well-known workaholic, Snowe is heavily involved in such major national issues as health care reform and tax policy but also on issues of unique interest to constituents in Maine. She delves into regulatory matters affecting Maine’s fishing industry through her post on the Committee on Commerce, Science and Transportation and is ranking member on the Small Business and Entrepreneurship Committee.

Amid an increasingly partisan atmosphere, Snowe has carved out a position as a lawmaker known for her willingness to work toward political compromise. She and Collins were two of three Republicans to support Obama’s roughly $787 billion stimulus package after Democrats agreed to trim billions from the original proposal. The pair were also heavily involved in the debate over a Wall Street reform bill and provided the votes necessary for Senate passage.

Snowe also forcefully opposed efforts to close the Portsmouth Naval Shipyard in Kittery during the last round of military base closings and has already ramped up her campaign to protect the shipyard in the coming round of closures.

At the same time, she has been rebuked by Democrats — including numerous times in the past year — for voting with her party on other occasions, such as when she voted against President Obama’s latest jobs bill and ultimately against the president’s health care overhaul.

The latter vote against Obama’s health care bill came after Snowe spent weeks working behind the scenes as a member of the Senate Finance Committee on a bipartisan compromise. Although she supported the committee’s bill, she joined other Republicans in voting against the final product after she accused Senate Democrats of substantially rewriting the bill and not allowing debate on the issue.

Although Snowe’s willingness to vote with Democrats on some major issues infuriated more conservative segments of the Maine GOP, she appeared to have strong support from many Maine voters, whether Republicans, Democrats or independents. She, along with Sen. Susan Collins, are often held up as examples of New England independence and pragmatism.

Politicians’ reputations at home are not necessarily the same as their reputations in Washington. But Scott Montgomery, editor of Roll Call, the news organization that chronicles all things political in Washington, said Snowe’s reputation on Capitol Hill and in Maine were largely one and the same.

Snowe is viewed as a very “substantive legislator” well versed on a wide variety of issues, he said.

“She is very well regarded,” Montgomery said. “She is known as an extremely hard worker,” adding that staffers in Snowe’s office don’t dare complain about their workload because the senator is typically working just as hard, or harder.

While Snowe’s announcement that she was dropping her re-election bid seemed to surprise pretty much everyone in politics, both in Maine and nationally, her cited reasons for doing so were not surprising. Snowe has repeatedly lamented the rancorous tone in Washington as the two parties became more deeply entrenched and less willing to broker bipartisan compromises.

“It’s not healthy for the country to have parties with polar opposite views without that bridge that you need to build consensus,” Snowe said in an April 2009 interview with The Associated Press on the gridlock in Washington. Addressing her willingness to cross party lines, she added, “It doesn’t mean abandoning your principles. It means trying to solve problems that people face in their daily lives.”

Collins has expressed similar dissatisfaction with the tone in Washington. But while many people believe the current level of partisanship is a new low for Congress, Snowe isn’t the first prominent Maine politician to decide to leave Congress due to the political atmosphere.

“At the end of the day, that is why Bill Cohen threw it in and, of course, that was 20 years ago,” said Christian Potholm, a political science professor, author and Republican pollster from Bowdoin College, referring to former Sen. William Cohen.

Snowe, for her part, has been operating as a moderate swing vote both during Obama’s presidency and during the administration of George W. Bush, and was often the target of criticism by whichever party ended up feeling slighted by her vote.

“It is not easy being a moderate Republican in Washington today,” Potholm said. “You have to [watch] your back as well as your front.”

In some ways, Snowe’s statement on Tuesday did echo Cohen’s sentiments when he shocked many by abruptly announcing in 1996 that he would not seek re-election. Writing in an OpEd published in the Bangor Daily News, Cohen said he and others who were leaving the Senate at the time “share a common level of frustration over the absence of political accord and the increase in personal hostilities that now permeate our system and our society.”

“We are witnessing a gravitational pull away from center-based politics to the extremes on both the right and left,” Cohen wrote.

Jim Melcher, a political scientist at the University of Maine at Farmington, said Snowe’s frustrations with both parties are well known but her sudden withdrawal from the race was surprising.

“It’s a very late time to be pulling out, and it certainly doesn’t seem like she had a successor anointed,” Melcher said. “If she had said this last September or October I wouldn’t have been as surprised.”

Roll Call’s Montgomery said Snowe’s withdrawal from the election is a “big, big deal” for another reason in that she is just the latest in a line of old-school, moderate lawmakers from both parties to opt to leave Congress this year.

Her departure also complicates Republican hopes to win back control of the Senate because, by Wednesday morning, many political observers had reclassified Maine from “safely Republican” to either a toss-up or leaning Democratic.

“We don’t know all of the factors that went into her decision but we know from her statement that she was fed up,” he said. “And for a legislator like her to be fed up is really bad news, whether you agree with her or not” on policy issues.

But Montgomery noted that similar concerns were raised immediately after Cohen’s decision to step away in 1996, which opened the political door for Collins. Snowe’s departure could, in turn, elevate Collins’ status as one of the last moderate Republicans left in the Senate.

Asked for his prediction on how things will look in Congress following the departure of so many moderate lawmakers, including Snowe, Montgomery wasn’t exactly optimistic.

“They are going to look worse,” he said.