Mike Michaud’s toughest race for U.S. Congress was his first.

Ten years ago, in 2002, the silver-haired Democrat out of Millinocket narrowly beat Republican Kevin Raye for an open seat in Maine’s 2nd Congressional District. Now, Michaud and Raye are facing off for the second time, in what observers say could be the toughest race of Michaud’s political career.

Raye’s campaign contends Michaud is vulnerable this time around: Voter demographics in the 2nd District have shifted in Raye’s favor during the past decade. That may be true, but observers say it’s extremely difficult to unseat an incumbent congressman, especially one as popular as Michaud. Raye is a serious contender, they say, but it might not be enough. A recent poll has Raye trailing by 19 points.

“There’s a lot to like about Raye as a candidate, and there’s a lot to like about the conditions of this district for a Republican,” said Mark Brewer, a political science professor for University of Maine. “I think it could be a tight race, but — all things being equal — incumbents have an advantage, and Michaud’s got the advantage.”

The numbers

In this campaign, Raye has been touting the party affiliations of state senators in the 2nd Congressional District as evidence of a turning tide.

He may be on to something: 15 out of 19 state senators in the 2nd District are Republican.

During the last election, Republicans living in the 2nd District picked up four out of five open seats and unseated three Democratic incumbents, according to records from the secretary of state. Ten years ago, when Raye lost to Michaud by about four percentage points — 9,019 more votes out of 224,717 cast — state senators in the same area were evenly divided between the two parties.

Anthony Corrado, a political science professor at Colby College in Waterville, said the Republicans who scooped seven seats in 2010 were riding a populist wave that might not exist into this election cycle.

James Melcher, professor of political science at University of Maine at Farmington, agreed the majority might not indicate a sea change in the district.

“It indicates that 2010 was a really good year to be a Republican in Maine,” he said.

According to voter rolls from the secretary of state, the composition of registered voters has shifted slightly toward Raye’s favor since the first match.

As of June, Democrats still outnumbered Republicans by 4,800 in the district; however, Republicans picked up 426 voters, while Democrats lost more than 5,000. Unenrolled voters, or independents, lost more than 4,000. There are 165,804 unenrolled, 137,056 Democrats, 132,256 Republicans and 15,531 Green Independent voters.

Overall, voter registration is down in the district by 455 people, with the only significant growth in the Green Independent Party, which picked up more than 8,000 voters since 2002.

The biggest voting bloc in the 2nd District is still unenrolled voters. They outnumber registered Democrats by more than 28,000, which could make this anyone’s race. However, they will likely go for Michaud, Melcher said.

“All things being equal, independents will tend to break toward an incumbent member of Congress unless they have a reason not to,” he said. “It’s just really hard to knock off an incumbent who hasn’t had a scandal, and there’s really no scandal there.”

At the same time, Green Independents aren’t necessarily a lock for the Democrat, Melcher said.

“Greens can be unpredictable,” he said. “I would say a majority would vote for Michaud, but I think it would be a mistake to say every one is going to vote that way. Raye isn’t the kind of Republican that’s going to rub Greens the wrong way. He’s not out denying global warming or primarily running from a socially conservative standpoint.”

Corrado said shifts in voter numbers ultimately don’t add up to much.

“That the district that has had some slight changes in voter enrollment is not as important as the fact that Congressman Michaud has a well-established identity in the district and is generally seen as well-aligned with the interests of the voters,” Corrado said. “It’s a district where jobs and the economy tend to be issue number 1 — not just this year, but in past elections — and Congressman Michaud, I think it’s fair to say, has worked hard to improve job prospects.”

The district lines have also shifted over the past years. In 2004, heavily Democratic Waterville was added to the district, as well as Winslow, but they have moved back to the 1st District for this election. Eleven smaller communities — Albion, Belgrade, Gardiner, Monmouth, Mount Vernon, Randolph, Rome, Sidney, Unity Township, Vienna and West Gardiner — were moved to the 1st District.

The candidates, then and now

In 2002, Raye’s political experience included 17 years working for Sen. Olympia Snowe, with seven years as her chief of staff in Washington. Michaud had served in the Maine House of Representatives for seven terms beginning in 1980, then served four terms in the state senate, beginning in 1994. He also was senate president in 2000.

Observers agree that both Raye, 51, and Michaud, 57, are more polished than when they first campaigned against each other, but Michaud’s 10 years in Washington outweighs Raye’s eight years in Augusta.

“Raye’s a stronger candidate than he was, but so is Michaud. Michaud’s got all those years of being in Congress, building up his name recognition, doing all the constituent service,” Melcher said. “Raye’s built up his name recognition also, by being state senate president. He’s very likable, but if you compare the advantage of having served in Congress — no matter what party you are — that’s a bigger gain than anything you could do in the state legislature. Plus, Michaud is more moderate than a lot of Democrats in other parts of the state.”

In 2004, Raye ran unopposed for state senate, and has maintained his spot for four terms despite challengers in each subsequent election. In 2006, in a four-way race, Raye won re-election with 59 percent of the vote. In 2008, during a three-way race, Raye won with 63 percent. In 2010, Raye won against a single challenger with 69 percent, according to state records.

Brewer said Raye’s campaign experience is unlike anything Michaud has faced before in a congressional race.

“I don’t think there’s any doubt that this will be Michaud’s toughest race since Raye vs. Michaud round 1. Since that first race, which was for an open seat, (Michaud) hasn’t really been terribly tested,” he said.

After beating Raye by four points in 2002, Michaud won re-election four times. In 2004, he won 58 percent of the vote in a three-way race; 70 percent in 2006; 67 percent in 2008; and 55 percent in 2010 amid a wave of Democratic defeats elsewhere in Maine and the country.

Brewer said Raye has a chance in 2012.

“There’s no doubt that a Republican could conceivably win the 2nd Congressional District — you don’t have to stretch the imagination too much,” Brewer said. “Kevin Raye is a tough candidate; he’s a quality candidate; he has relatively high name recognition; he comes from the stock line of one of Maine’s most popular politicians (Snowe).”

Still, a recent poll bodes poorly for the Republican challenger, Melcher said. On Thursday, the Maine People’s Resource Center released results from a survey of 410 registered voters in the 2nd District, which showed Michaud leading Raye, 56 percent to 37 percent.

“That’s a lot of ground to make up,” he said. “At this point, Raye is pretty well known, I mean there hasn’t been a lot of TV advertising yet, but that wouldn’t seem to be extremely encouraging for him,” Melcher said.

To get ahead, Raye might have to mount a negative campaign, but Melcher thinks that’s unlikely.

“They already have to a certain extent. They were very critical of Michaud’s campaign commercial,” he said. “In terms of running negative ads, though, it doesn’t seem like Raye’s style. I would say he’s less likely to do that than some people, but you couldn’t rule it out.”

In the meantime, with 44 days left until the election, anything can happen. Melcher said he expects Raye to receive financial backing from national organizations, and cited recent endorsements from the National Federation of Independent Business and the U.S. Chamber of Commerce as signs of potential growth.

“It’s a competitive race,” Melcher said. “They’re both on their game, no doubt about it.”