The race to represent Maine in the 1st Congressional District has heated up in recent weeks with more advertising, stinging rhetoric and upcoming debates.

U.S. Rep. Chellie Pingree is trying to fend off two challengers, independent Martin Grohman and Republican Mark Holbrook, to defend her seat in Congress. The North Haven Democrat has held the seat since 2009.

Whether either has a legitimate shot at beating Pingree in the Nov. 6 election is unknown, as there’s been a dearth of public polling on the race. The first debate among the three candidates is at noon Wednesday at WMTW-TV in Westbrook. The other two debates will be at 8 p.m. Oct. 22 at WCSH-TV in Portland and the Maine Public debate at 6 p.m. Oct. 30.

Michael Franz, a professor of government and legal studies at Bowdoin College, said Pingree is still the heavy favorite. He said Grohman, a former Biddeford lawmaker, has an uphill battle to obtain enough name recognition with voters to consider pulling the lever for an independent over a Republican or Democratic candidate. Republicans also typically have a difficult time winning in the 1st District, a congressional district in southern Maine that’s more liberal than Maine’s 2nd District. In 2016, Pingree defeated Holbrook by a 58 to 42 percent margin.

“Grohman’s path to victory is very narrow,” Franz said. “I haven’t seen enough from him yet to suggest Pingree is being knocked off course.”

Grohman has been very active in recent weeks, releasing ads, collecting endorsements and attacking Pingree over her voting record regarding Bath Iron Works. Grohman is arguing that Pingree voted against funding for BIW at certain points, dating back to 2011. Riley Ploch, Grohman’s spokesman, said workers are feeling “betrayed” because Pingree is voting against their livelihoods.

“She has voted against BIW funding at every step of the funding process,” Ploch said.

But Eric Feigenbaum, Pingree’s campaign manager, said Grohman’s criticisms are misleading, because the defense appropriations bills contain many aspects of funding, and when she’s voted “no” it has nothing to do with Bath Iron Works.

Feigenbaum said Pingree helped save $250 million for a Bath Iron Works defense contract this summer that was “on the chopping block.”

“When funding for BIW was under threat, she went to bat for BIW in a big way,” Feigenbaum said.

Holbrook, on this issue, took Pingree’s side, calling Grohman’s attacks “disingenuous.”

“This is a feeble attack by Grohman to cast himself as a hero,” Holbrook said in a phone interview Monday. “There’s a lot of things to criticize Pingree about, but that’s not one of them.”

An unknown in the congressional race is ranked-choice voting, which is being used for the first time in federal races in Maine this fall.

In ranked-choice voting, voters can choose to rank the candidates. In the 1st District race, voters would rank candidates one through three. If no one receives a majority of the votes on the first ballot, the last-place candidate is eliminated, and voters’ second-place choice for the last-place candidate is reallocated among the remaining candidates.

Ploch said Grohman campaign’s strategy is, if Grohman doesn’t win outright, to keep Pingree under 50 percent and finish in second place. He said he believes most of Holbrook’s second-place votes – presumably conservative Republicans – would go to an independent over a Democrat, putting Grohman over the top.

Franz said while ranked-choice voting is an “x factor,” he has a hard time seeing enough Republicans abandoning Holbrook to put Grohman in second place, and he believes Democrats will mostly stick with Pingree.

Pingree, for her part, is running television advertising this year, unlike in 2016, when she stayed off the airwaves. Feigenbaum said Pingree is emphasizing kitchen table issues such as lowering the cost of prescription drugs and preserving the Affordable Care Act.

Ploch said it’s hard to believe that Holbrook is running a serious campaign, based on what he’s seen of Holbrook’s activity and the lack of a campaign manager.

Holbrook said he’s his own campaign manager.

“I’m not (wasting) away a bunch of money on paid staff,” Holbrook said. “People are volunteering for me because they believe in the Constitution and believe in me.”