WASHINGTON — Maine was supposed to be one of the easy states.

As Republican leaders on Capitol Hill laid out their strategy for retaking the Senate, Maine was considered a near lock for the party, thanks to Sen. Olympia Snowe’s longevity and cross-party appeal back home. And then came Snowe’s surprise Feb. 28 announcement.

“After an extraordinary amount of reflection and consideration, I am announcing today that I will not be a candidate for re-election to the United States Senate,” Snowe said, citing the political polarization in Congress.

“In essence, Olympia Snowe’s retirement is one of the great bumps in the road that has impeded the Republican path to 50 (seats),” said Larry Sabato, an election prognosticator with the University of Virginia’s Center for Politics. “It is becoming increasingly obvious that they are not likely going to win control of the Senate,” Sabato said, and Snowe’s retirement “helped to change the momentum.”

Snowe’s decision also shook Maine’s political map like an 8.0 magnitude earthquake, briefly threatening to rewrite the ballots for the state’s two House races and eventually leading to a six-person Republican primary and a four-person Democratic primary.

What followed has been one of the most closely watched Senate bouts in the nation, and one of the most unconventional races in Maine history.

Republican groups ran ads to boost a Democrat. National Democrats all but ignored their own nominee in favor of a left-leaning independent. Out-of-state billionaires dumped huge sums into ads on both sides. And Snowe — whose approval rating often approaches 70 percent — has steered clear of campaigning with Republican candidate Charlie Summers, a former member of her staff, even while helping Senate Republicans in other states.

DOWN TO THREE

Independent Angus King, Summers and Democrat Cynthia Dill are now the three top candidates seeking Snowe’s seat, with King believed to be leading the group by a safe margin. Three other independents — Danny Dalton, Andrew Ian Dodge and Steve Woods — are also on the ballot.

But after months of television ads — including $7 million purchased by outside groups alone — it is easy to forget that at one point many of the biggest names in Maine politics were considering a run.

On the Democratic side, former Gov. John Baldacci and U.S. Reps. Chellie Pingree and Mike Michaud all gathered signatures to qualify for the ballot. But each ultimately decided against it, some reportedly at the urging of national Democratic leaders concerned about handing Summers a victory by splitting the liberal and moderate vote.

State Senate President Kevin Raye, a Republican running to displace Michaud in the 2nd District, considered joining the fray. And for a few days in March, political junkies were buzzing not over whether an independent would run for the Senate but which independent: King or Eliot Cutler?

Personal friends, King and Cutler — who fell two points short of winning the governor’s mansion in 2010 — reportedly talked it over before King decided to enter the race. Cutler, meanwhile, signed on as one of King’s statewide campaign chairmen as he gears up for another gubernatorial run in 2014.

But there were also rumors of another agreement — this one between King and Democratic leaders in Washington. The former governor has forcefully denied any suggestions that he has pledged to caucus with the Democrats, if elected.

“As I said the night I announced, no one is going to tell me how to vote except the people of Maine,” King said after Democrats launched television advertisements widely regarded as helping him.

AHEAD FROM THE GET-GO

Even before the Republican and Democratic primaries were over, it was clear that King would be the candidate to beat come November. With his easy-going style, politicking skills and iconic mustache, King entered the race with a significant name-recognition advantage and an electorate that generally seemed to remember liking him as governor a decade ago.

Media companies from New York to Washington and Los Angeles sent crews to Maine to tag along with the independent candidate who could help decide which way the Senate leans. King also quickly became the target of the first negative ads — back in July — as the U.S. Chamber of Commerce criticized King’s record as governor and his wind energy business.

King proudly declared that he was running for the Senate for the very reasons Snowe was leaving — Congress’ hyper-partisanship and unwillingness to compromise even when dealing with the nation’s gravest challenges. Yet King has insisted that, as an independent not beholden to serving in either trench, he could wield disproportionate power.

Playing on Maine’s independent streak, King has steadfastly refused to say with which party he would caucus if elected, despite being asked constantly by reporters, debate moderators and voters.

King’s caucus non-committal has prompted some skeptics — including Maine Democratic Party leaders who are backing Dill — to question whether progressive or left-leaning voters would be taking a gamble with King. Most political observers believe King will side with the Democrats, given his support for President Obama, backing of Obama’s health care law, support for abortion rights and other stances.

But King’s vagueness could add a wrinkle to Election Day if the fight for the Senate is close.

“Maine might be part of the reason we don’t know who will be in control of the Senate on election night,” said Nathan Gonzales, deputy editor at The Rothenberg Political Report, a D.C.-based newsletter. “I don’t think there is any debate on whether he will caucus with the Republicans or the Democrats, but I don’t think he will make an election night announcement.”

MOST OUTSIDE MONEY

Maine’s high-stakes Senate race has attracted big money from out of state.

Although likely to fall short of the record $14 million spent in the 2008 race between Republican Sen. Susan Collins and Democratic former U.S. Rep. Tom Allen, the 2012 race has drawn more outside money than any past race. In fact, outside interests have outspent the candidates themselves by a significant margin, thereby changing the debate and tone of the race.

As of Friday, outside groups operating independently of the campaigns had spent $7.3 million in Maine. The Democratic Senatorial Campaign Committee was leading the pack with roughly $1.5 million spent on anti-Summers ads, followed by the U.S. Chamber and the National Republican Senatorial Committee, each of which spent about $1.3 million on ads attacking King.

Two more recent arrivals to the race are Americans Elect — a nonpartisan group supporting King that is funded by New York City Mayor Michael Bloomberg and two other billionaires — and Karl Rove’s conservative group Crossroads GPS, which opposes King and supports Summers.

Americans Elect has already spent $1.3 million of the $1.75 million pledged to help King while Crossroads GPS has spent roughly $1 million. That led The New York Times to write last week that “the Maine Senate race has become so convoluted that at times it has seemed as if Karl Rove and Michael R. Bloomberg were running against each other.”

Summers and King have also courted wealthy out-of-state donors, with both attending fundraisers in Washington and King benefiting from an event thrown by Bloomberg at his Manhattan residence.

But the outside groups have provided some of the twists and turns that made Maine’s Senate race so unusual. The Republican-aligned Maine Freedom PAC, for instance, aimed to help Summers by driving more voters to Dill with ads praising her as the “real progressive.” The Democratic committee, meanwhile, aired more than 1,000 anti-Summers ads presumably to help not the Democrat but King, whose lead was shrinking.

REPUBLICANS STILL SPENDING

Yet after more than $10 million in spending by all parties, polls suggest that while the numbers have shifted, the order remains the same: King leading Summers by double-digits with Dill trailing in third.

“I don’t think a lot of that made a big difference,” said Kenneth Palmer, a professor emeritus of political science at the University of Maine, of the unconventional advertising tactics. “Even with all of the outside spending, I don’t think that changed things very much. Angus started out very well and I think he will win.”

The National Republican Senatorial Committee, the U.S. Chamber and the Democratic Senatorial Campaign Committee have largely pulled out of Maine and diverted their money to more competitive races.

But not all Republican groups have given up on retaining ownership of Snowe’s Senate seat — or at least intend to put up a solid fight to the end for it.

Crossroads GPS paid another $335,000 last week for additional anti-King ads to run through Election Day. And a new conservative group, Safe Nation PAC, spent just shy of $35,000 on mailers and radio ads meant to provide Summers with last-second boost.

Safe Nation PAC, which is based in Georgia, appeared to be employing a split-the-vote strategy in the mailers, which portray Dill as a solid progressive over King. But their radio ads, which will run through Election Day, tout Summers’ military career and work as Maine’s secretary of state.

“A judgment was made on whether or not the Senate race was in play, and it is,” said R.C. Hammond, a spokesman for the PAC. “Charlie is a very good candidate, and there’s an opportunity where a difference can be made.”

Washington Bureau Chief Kevin Miller can be contacted at 317-6256 or at: kmiller@pressherald.com

Twitter: @KevinMillerDC