PORTLAND — The first of several debates by the candidates for Maine’s 1st Congressional District revealed differing takes on subjects as varied as recreational marijuana and the best way to combat ISIS terrorists.

All three candidates — incumbent Democrat Chellie Pingree, Republican Isaac Misiuk and independent Richard Murphy — attended the televised debate hosted by the Bangor Daily News and CBS 13 at the television station’s Portland studio.

Pingree said that she would categorically oppose any effort to expand President Barack Obama’s campaign of airstrikes against Islamic State, or ISIS, to include a ground troop campaign.

She said the rise of ISIS — which has beheaded Western journalists and aid workers, and slaughtered and terrorized communities in Iraq and Syria — was at least partially the result of the U.S. invasion of Iraq in 2003, which she opposed.

“We shouldn’t have gone there in the first place,” said the 59-year-old North Haven resident and incumbent three-term congresswoman. “We made enormous mistakes as a country doing what we did, and we set off a chain of events that we’re still facing today.”

Misiuk, a 25-year-old Gorham resident and sophomore at the University of Southern Maine, said he knew his stance in favor of a ground war against ISIS would not be popular, but that it was the only tenable option.

“The problem is, right now, in the history of any conflict, airstrikes alone have not won any war,” he said. “Everyone expects a feel-good answer, but the fact of the matter is the only way to contain this is send ground troops, unfortunately.”

Murphy, a 37-year-old Sanford native and National Guard member who has served two tours in Iraq, said the U.S. no longer should be involved in the Middle East. He seemed especially irked by the idea of sending ground troops to battle ISIS.

“If either one of you are elected this time around, and you talk about sending boots on the ground, you’re talking about sending me,” he said. “And I do not appreciate that.”

Murphy, an independent with a libertarian bent, was the wildcard in the debate. On some issues, he sided with Pingree, a progressive Democrat, while on others he agreed with Misiuk, who usually but not always held the Republican Party’s line.

Both Misiuk and Murphy said they’d welcome the temporary construction jobs created by transporting tar sands through Maine. Pingree opposes the idea, citing environmental concerns and saying Maine should focus instead on renewable energy.

On the federal legalization of recreational marijuana use, it was Pingree and Murphy who aligned, both saying they’d agree with legalization, while Misiuk was opposed.

On the Affordable Care Act, Murphy was the only candidate who said he’d support House Republicans’ efforts to repeal and replace the president’s landmark 2010 health care reform bill. Misiuk said that while he opposed some of Obamacare, voting to repeal the law now, four years later, would be fruitless because the reforms contained in the act are too “entrenched.” Pingree defended the act, though she said she didn’t think it went far enough.

The only issue the candidates all agreed on was climate change: All three said they believe the threat of climate change is real and is caused by human activity.

While the debate was at times lively, the dynamics of the race heavily favor Pingree. She is buoyed by the tide of liberal voters in the left-leaning southern district and by a significant polling and fundraising advantage over her two challengers.

A University of New Hampshire poll commissioned by the Portland Press Herald late last month showed that Pingree’s lead had only grown since its earlier survey in June, with Pingree leading Misiuk 66 percent to 13 percent, with Murphy barely moving the needle.

On the campaign finance front, Pingree’s lead is similarly dramatic. By the end of June, when the last filing period ended, the Democrat was sitting on a war chest of more than $314,000. Misiuk had just $1,300 cash on hand, while Murphy’s fundraising effort seems nonexistent.

Outside groups also seem confident that little could be done to change the dynamics of the race: Not a single independent expenditure has been reported in the 1st Congressional District, according to the Federal Election Commission. Contrast that with the 2nd Congressional District, where a tight race has drawn more than $1 million in spending from third-party groups trying to tip the scales.

The three candidates for the 1st Congressional District will meet twice more for televised debates, first on Thursday, Oct. 9, on MPBN, and later in the month on WCSH-TV.