Reps. Stephen Lynch (D-Mass.) and Edward MarkeyEdward (Ed) John MarkeyRegulators seek to remove barriers to electric grid storage Markey, Paul want to know if new rules are helping opioid treatment Oil spill tax on oil companies reinstated as part of budget deal MORE (D-Mass.) again struggled to find points of difference in their second televised debate in the Massachusetts Democratic primary for the U.S. Senate on Monday night.

The two candidates for the seat vacated by Secretary of State John KerryJohn Forbes Kerry2020 Dem contenders travel to key primary states When it comes to Colombia, America is in a tough spot 36 people who could challenge Trump in 2020 MORE faced off in front of an energetic crowd of college students at the University of Massachusetts Lowell, just three weeks out from primary day.

Though both candidates have signed a pledge to keep outside money out of the contest, the Massachusetts Senate race has received an influx of more than $1.26 million in spending from outside interests, much of it from a single California billionaire, Tom Steyer, who opposes the construction of the Keystone XL pipeline and has attacked Lynch for his support of it.

Lynch, in a shift from his initial support of the pipeline, said he's waiting to see what the environmental impact report says. And in one of his biggest applause lines of the night, he decried Steyer's influence

"Just because he has a billion dollars does not mean he gets to push people around. I've faced bullies my whole life, and I won't put up with that," he said.

Markey noted that he's asked Steyer to stay out of the race.

In answer to a question that hadn't yet been raised in the race, both criticized President Obama's use of drones, with Lynch noting his many trips abroad to visit troops, and calling the president's use of drones "incautious."

“What we’ve done here is, by incautious use of drones, we’ve really hurt ourselves, hurt our standing in many ways,” he said.

Markey praised Sen. Rand PaulRandal (Rand) Howard PaulDem wins Kentucky state House seat in district Trump won by 49 points GOP's tax reform bait-and-switch will widen inequality Pentagon budget euphoria could be short-lived MORE (R-Ky.) for his 13-hour talking filibuster of CIA Director John Brennan's confirmation, during which Paul raised the question to national prominence.

“It’s a good way to use the filibuster in the Senate,” he said.

But both stumbled on other issues in the debate, with Lynch in particular struggling to explain his evolution on gay rights.

Both said they support a constitutional amendment to make same-sex marriage legal nationwide, but Lynch stumbled when responding to a question about his previous stance in opposition to benefits for same-sex couples.

Lynch, during his time as a state lawmaker, opposed measures to expand benefits to partners and to strengthen hate crimes legislation.

"I don't recall that, specifically, but if it was a question of payments, I could have voted in a way that was not consistent with gay coverage, I guess. But I'll tell you what my position is right now and if it was 16 years ago or 17 years ago if I voted to interfere with that, I was wrong," he said, noting his work on gay rights during his time in Congress.

Markey, when asked about his relationship with a campaign adviser who is lobbying for approval of the Keystone XL pipeline, didn't distance himself from the aide, Larry Rasky. He insisted, however, that his views were his own.

"It doesn't make any difference to me whether one of my supporters [has] a different view," he said.

Markey also had the opportunity to answer a common critique of his candidacy: That he's lived so long away from Massachusetts, he's lost touch with his constituents. Though he owns a home in his district, he spends much of his time at his home in Maryland.

"The people in Massachusetts, the people in my district, know that I have gone to Washington to fight those fights animated by the values of Malden, Mass., where I grew up and where I live today," he said.

One main contrast came during a question surrounding funding for research, which allowed Markey to highlight his vote against the series of across-the-board budget cuts known as sequestration.

"Sequestration is just another word for cuts, mindless cuts," he said, calling research "medicine's field of dreams from which we harvest the findings that give hope to families" suffering from diseases.

Markey said that he's led an effort in Congress to restore and expand funding for the National Institutes of Health.

Lynch, for his part, said he voted for sequestration — included as part of the Budget Control Act of 2011, which also increased the debt limit and passed with support from a majority of Republicans and half the Democrats in the House — to prevent the country from defaulting on its debt.

"The $16.7 trillion in debt we have right now is on you, it's on your backs," Lynch said to the college crowd, "and it's threatening our ability to maintain a decent standard of living in this country."

The two closed with autobiographical remarks, both framing themselves as products of a working-class upbringing fighting for average Massachusetts citizens.