Reps. Donna F. Edwards and Chris Van Hollen. (Mark Gail/For The Washington Post)

Reps. Donna F. Edwards and Chris Van Hollen clashed Tuesday over the role of super PACs in their hard-fought Democratic primary race for a rare open Senate seat in Maryland.

At a debate televised by WJLA (Channel 7), Van Hollen attacked Edwards for refusing last summer to sign a pledge barring super PAC involvement in the contest and again urged her to sign it — even though outside groups made possible by the Supreme Court’s 2010 Citizens United decision have spent heavily on behalf of both candidates.

“Why don’t you join me in putting your name to what you stand for?” asked Van Hollen, who like Edwards opposes the Citizens United decision.

Edwards countered that she is “proud” to have the support of a super PAC run by Emily’s List, a group committed to electing female Democrats who support abortion rights and which has committed $2.4 million to the race so far.

The group’s first candidate, Edwards noted, was retiring Sen. Barbara A. Mikulski (D), whom she and Van Hollen are vying to replace. “They stood on the side of Barbara Mikulski when the political establishment said she couldn’t win, in a race very similar to this one,” Edwards said.

Van Hollen, she suggested, has less-desirable super PAC backing. The National Association of Realtors has in recent days spent nearly $1 million in support of the congressman, including $384,000 on television spots, $370,372 on mail to voters and $126,000 on online advertising.

Emily’s List does not lobby members of Congress, Edwards noted. The realtors’ group does, contributing heavily to Republican and Democratic candidates.

“They don’t expect anything in return,” Edwards said of Emily’s List. “What do the realtors expect from you?”

Van Hollen pointed out that Edwards has also taken money from the realtors’ group — $25,000 over her eight years in Congress. At a forum Monday night in Baltimore, Van Hollen chided Edwards for appearing to approve of some outside groups and not others.

“If you’re against Citizens United, you don’t get to pick which super PAC you like and which one you don’t like,” he said.

He said more than half of the money collected by the Emily’s List super PAC this cycle has come from Wall Street — true if you include all hedge-fund managers and their spouses under the “Wall Street” umbrella, regardless of their locations.

Of the $4 million raised by Women Vote for the 2016 election, $1.5 million came from S. Donald Sussman, a Florida-based hedge-fund manager and a major Democratic donor. An additional $500,000 came from Marilyn Simons, wife of hedge-fund manager James Simons. Billionaire and former New York mayor Michael R. Bloomberg contributed $40,000.

Van Hollen has raised far more money than Edwards; at the end of last year he had 10 times as much cash on hand.

The two candidates also sparred at the forum over a bill Van Hollen introduced in 2010 that would have required greater disclosure from outside groups.

To improve its chance of passage, Van Hollen agreed to exempt the National Rifle Association and the Sierra Club from the strictures. In response, Edwards pulled her support for the bill and spoke against the legislation. “The biggest, baddest actor in this system is the NRA,” she said Monday.

Van Hollen noted that “the vast majority of Democrats,” including Mikulski and Rep. Elijah E. Cummings (D-Md.), backed his bill, which despite the changes failed to garner Republican support and died in the Senate.

Van Hollen touted his record on gun control, saying he had passed gun-safety legislation at the state level and introduced it at the federal level.

At both the debate and the forum, the candidates also revisited more familiar points of tension.

Edwards accused Van Hollen of betraying progressive values on criminal-justice reform, trade deals and negotiations over the budget. Van Hollen said those attacks were distortions. He is a co-sponsor of sentencing reform legislation in the House, he noted, while Edwards is not.

As the ranking Democrat on the House Budget Committee, Van Hollen said, he was trusted by his colleagues to lead the fight to protect Social Security and never supported any cuts. And he noted that several unions very concerned about foreign trade, such as the United Auto Workers, have endorsed his campaign.

“I’ve been running on my record, and Congresswoman Edwards has been running away from her record,” he said Tuesday.

Van Hollen accused Edwards of failing to work with Republicans or respond quickly to residents of her district. He pointed to an op-ed in the Baltimore Sun by Heather Mizeur, a former state delegate and 2014 gubernatorial candidate, who wrote that Van Hollen has far outpaced Edwards in responding to constituent needs.

Edwards, in turn, called that charge “inaccurate,” citing the job fairs and college fairs she has held. As for bipartisanship, she said she worked with Republicans on NASA reauthorization as well as on transportation policy.

Correction: Earlier versions of this story incorrectly identified former state delegate Heather Mizeur as a former state senator. The article has been corrected.