Sen. Ed Markey Edward (Ed) John MarkeyDemocratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy McConnell says Trump nominee to replace Ginsburg will get Senate vote Massachusetts town clerk resigns after delays to primary vote count MORE (D) and Rep. Joe Kennedy Joseph (Joe) Patrick KennedyMassachusetts town clerk resigns after delays to primary vote count Bogeymen of the far left deserve a place in any Biden administration Hillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections MORE III (D) went head-to-head in Massachusetts's first Democratic Senate debate on Tuesday, kicking off what is expected to be a contentious intraparty battle this year.

While Markey and Kennedy agreed on most issues during the hourlong debate Tuesday night in Boston, the two progressive lawmakers sparred over style and experience as they made their case to Democratic voters ahead of the Sept. 1 primary.

"This is not a swing state. This is not a swing seat. There is a special opportunity and obligation that comes with it because voting the right way and filing the right bill? Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE doesn't care," Kennedy said at the start of the debate.

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"Given the challenges that we face, that you have to ensure that you are bringing everything you possibly can to restore power to a Democratic Party so that we can actually advance the causes we care about and protect the people that we care about," he said.

Markey, meanwhile, touted his experience on Capitol Hill, pointing to his work combating climate change and gun violence as well as working to find a cure for Alzheimer's.

"On the big issues of today, the challenges of today, I've not only been leading, but I've been delivering with legislation which passes, which protects the people of Massachusetts, and the whole country," the incumbent senator said.

Some of the more tense moments of the evening came when speaking about campaign finance reform and Markey's past votes on foreign intervention.

Kennedy drew attention to Markey's vote in favor of the Iraq War, which the senator said he regretted and blamed on "false pretenses" from the Bush administration.

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Markey also defended his "present" vote in 2013 on Syria strikes, referring to it as a "disinfectant" that provided senators with more information about the consequences of bombing Syria.

"Hard for me to understand that a 'present' vote is going to be a profile in courage," Kennedy responded.

The congressman continued to call on Markey to limit outside spending in the race by signing the People's Pledge initiative, which he has signed in years past.

"[If] you do not do this, how are you ever going to pass a Green New Deal if you allow the fossil fuel industry to open up the spigot and flood the airwaves with scare tactics?" Kennedy asserted.

"Look, we should not silence these progressive groups. We should encourage them," Markey responded. "If they want to come into this debate, speak positively, disclose their funding sources, we should welcome and celebrate them."

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Kennedy, 39, the grandson of former Attorney General Robert F. Kennedy, announced he was challenging Markey, 73, last year, basing his campaign on generational change in Washington.

While establishment Democrats, including Senate Minority Leader Charles Schumer Chuck SchumerPelosi orders Capitol flags at half-staff to honor Ginsburg Ginsburg in statement before her death said she wished not to be replaced until next president is sworn in Democrats call for NRA Foundation to be prohibited from receiving donations from federal employees MORE (D-N.Y.) and Democratic Senatorial Campaign Committee Chairwoman Catherine Cortez Masto Catherine Marie Cortez MastoDemocratic Senate campaign arm raised nearly M in August VA problems raise worries about mail slowdown, prescriptions Cortez Masto touts mail-in voting in convention speech MORE (D-Nev.) have expressed their support for Markey, Kennedy holds a lead in early polling and in fundraising.

Kennedy led Markey in fundraising in the final three months of 2019, raising $2.3 million and ending the year with $5.5 million cash on hand. Markey brought in $1.4 million in the same period and rounded out the year with $4.6 million cash on hand.

A Suffolk University-Boston Globe survey in September found that 35 percent of likely 2020 Democratic primary voters said they favored Kennedy, while 26 percent said they favored Markey.