Rep. Chris Van Hollen seems an unlikely target for a Democratic super PAC’s ­biggest-ever primary campaign. A rising star in the party, the Senate candidate is a longtime protege of House Minority Leader Nancy Pelosi and a high-profile defender of liberal policies.

But he’s also a man running against a woman for the Democratic nomination to succeed retiring Sen. Barbara A. Mikulski (D-Md.), the longest-serving woman in Congress. And so the pro-choice women’s group Emily’s List is committing at least $2.4 million from its super PAC — Women Vote! — to help Rep. Donna F. Edwards defeat him.

Emily’s List argues that its mission is to elect pro-choice Democratic women, regardless of who gets toppled along the way. The group says its investment on behalf of making Edwards Maryland’s first African American female senator helps continue the legacy of Mikulski, the first woman elected with Emily’s List support.

“Making history 30 years ago was just as important as it is today,” said Emily’s List spokeswoman Marcy Stech.

Van Hollen’s supporters, including Maryland State Treasurer Nancy Kopp (D), contend that instead of spending so much to back Edwards, Emily’s List should focus on helping female candidates running against Republicans who don’t support the group’s agenda.

Emily’s List Super PAC Women Vote released an ad endorsing Rep. Donna F. Edwards (D-Md.) for Senate. The ad praises her stance on regulating Wall Street. (WomenVOTEProject/ YouTube)

“I’m disappointed, like many other people, that Emily’s List has chosen to try to use its muscle to oppose a candidate who I think has represented Maryland really well,” said Kopp, a former state lawmaker who served with Van Hollen in Annapolis and has endorsed his campaign.

Van Hollen is the top Democrat on the House Budget Committee, and he has used that perch to protest Republican attempts to defund Planned Parenthood. He also has advocated paid family leave and equal-pay legislation. Four times as many female elected officials in Maryland are endorsing him as are endorsing Edwards.

Edwards, a progressive in her own right, has five fewer years in Congress than Van Hollen and has had lower-profile committee assignments. She has struggled to raise money on her own. But Emily’s List’s super PAC has launched a major television ad campaign on Edwards’s behalf that has matched or exceeded Van Hollen’s television effort, helping to keep the race competitive.

After weeks of the candidates’ running neck-and-neck, a Baltimore Sun-University of Baltimore poll this month gave Edwards a six-point lead. The candidates are meeting for their second debate in Baltimore on Friday.

[Van Hollen, Edwards on attack in first debate]

Van Hollen supporter Susan Esserman, a former deputy U.S. trade representative who lives in his district, said she was “shocked and deeply distressed” when she learned that Emily’s List was working against the congressman, who has always championed the group’s abortion-rights, pro-women agenda.

“I just thought in this case it showed misplaced priorities,” Esserman said. “We should be looking at our goals, which should be to elect more women but also to make sure that we have strong and effective people in place to advance women’s rights.”

Pelosi (D-Calif.), who is staying neutral in the Senate race, praised Emily’s List and both candidates but expressed a similar concern. “More women in the Senate — that's their goal,” she said. “I would hope that it’s not at the cost of more women in the House, when it’s between a Democrat and a Republican who will vote pro-choice, pro-gun safety.”

Debbie Walsh, director of the Center for American Women and Politics at Rutgers University, said the group’s efforts on behalf of Edwards make complete sense.

“For them, the priority is electing pro-choice Democratic women,” Walsh said. “The ‘woman’ part really matters to them.”

Some campaign-finance watchdogs argue that in a world where both black and female candidates have less access to power, Edwards might need more help.

“One candidate has a broad network of major donors due to his background and previous roles in the party,” said Adam Smith of Every Voice, which advocates public financing for campaigns. “The other candidate, due to her background and where she comes from, doesn’t necessarily have that same level of access.”

[Edwards: Why aren’t black women ever described as ‘born to’ the Senate?]

Such talk is endlessly frustrating for Van Hollen, who unsuccessfully sought an agreement with Edwards early in the campaign to ban spending from outside groups. He would not commit to the pledge unilaterally, though, and this week a super PAC run by the National Association of Realtors filed papers showing that it had spent more than half a million dollars supporting Van Hollen’s campaign.

His aides describe the huge lift Edwards is getting from the Emily’s List effort as ironic — and a sign of hypocrisy on her part.

Both Edwards and Van Hollen opposed the 2010 Supreme Court decision known as Citizens United, which legalized unlimited campaign spending by outside groups. Edwards was the first member of Congress to propose a constitutional amendment overturning it.

And although Edwards has positioned herself as an outsider and opponent of Wall Street, through Emily’s List she is benefiting from deep-pocketed donors who in several cases have corporate ties. According to the most recent federal filings, the group’s super PAC has taken more than $2 million this cycle from hedge-fund managers or their spouses, including $1.5 million from financier and Hillary Clinton supporter S. Donald Sussman.

Each Senate candidate has long-standing connections to Emily’s List. The group helped Edwards topple former Rep. Albert R. Wynn (D) in 2008, making a rare endorsement of a challenger to a Democratic incumbent. A former Emily’s List political adviser, Garrick Delzell, is managing Edwards’s Senate campaign.

As for Van Hollen, many of his stalwart donors are contributors to Emily’s List. Sheila O’Connell, his campaign manager, used to work as the group’s political director. The polling firm employed by Van Hollen’s campaign also does work for Emily’s List’s super PAC.

“Maryland women are asking why Emily’s List is spending millions against a leader like Chris instead of on other races where their priorities are in jeopardy,” said Van Hollen spokeswoman Bridgett Frey, who has repeatedly accused the advocacy group of “trying to buy a U.S. Senate seat.”

Edwards declined to discuss the group’s work on her behalf. In a statement, the campaign said Emily’s List “was there for Senator Barbara Mikulski from the beginning. Thirty years later, we’re proud to have their support.”

Super PACs are not allowed to coordinate with campaigns, but there are ways to circumvent those rules. Emily’s List has used video that Edwards’s campaign posted to YouTube. Watchdogs consider that illegal coordination; the Federal Election Commission is split on the issue.

Emily’s List can also telegraph its moves through news releases — for example, announcing a million-dollar ad commitment in Maryland, as the group did this month, which let Edwards know she doesn’t have to worry about television spending.

Van Hollen’s fundraising appeals have lamented the use of “dark money . . . right on our doorstep.” The campaign sent letters to Emily’s List donors suggesting that the group had gone astray, which prompted Emily’s List to file a complaint with the Federal Election Commission, where it is pending.

Van Hollen’s request last summer that Edwards sign a pledge barring outside groups from spending in the race was a not-so-subtle attempt to stop the flow of Emily’s List funds. She quickly rebuffed him, calling the pledge “laughable.”

In fact, Van Hollen faced a similar offer back in 2002, when he ran against Rep. Constance A. Morella, a popular incumbent and moderate Republican whom he ended up beating.

Morella wanted to keep soft money — independent money from political parties — out of the race. Van Hollen, then a state lawmaker, pointed out that he needed support from those groups, because Morella had far more money in her campaign bank account.

“It’s a phony stunt,” Steve Jost, manager of Van Hollen’s 2002 campaign, said at the time.