A pair of attack ads paid for by shadowy, third-party groups stirred the high-profile contest for Maryland's open Senate seat Tuesday, underscoring the limits of disclosure rules and leaving the candidates in the Democratic primary bracing for a potential onslaught in the final weeks of the campaign.

Two super PACs that had operated on the periphery of the race for weeks launched attack ads on broadcast television in Baltimore. One accused Rep. Donna F. Edwards of being ineffective; the other suggested that Rep. Chris Van Hollen caved to the gun lobby during a negotiation six years ago.


Both came from groups that have not yet disclosed their donors — and both offered an incomplete picture of the record.

Democratic Rep. Steny Hoyer of Southern Maryland, who has not endorsed a candidate in the competitive primary race, took the unusual step of calling on the group airing the anti-Van Hollen ad to take it down.

Jennifer Bevan-Dangel, executive director of Common Cause Maryland, said that "these types of ads represent the worst of our campaign finance laws.

"Because of loopholes in our law, these ads can run without any accountability or disclosure to make sure voters at least know who is behind them — and why."

The primary election is April 26. Early voting begins Thursday.

An NBC4/Marist Poll released on Tuesday showed Van Hollen of Montgomery County with a six-point lead over Edwards of Prince George's County.

One of Maryland's most politically powerful unions, 1199SEIU, revealed Tuesday that it had created one of the groups: the Committee for Maryland's Progress. It said it is airing the anti-Edwards ad because its leaders feel they were let down by the 4th District congresswoman.

The health care workers union, which has 9,000 members in Maryland, helped propel Edwards to victory in her primary challenge to Democratic Rep. Albert R. Wynn in 2008. The group shocked the state's political establishment when it announced that in December it was backing Van Hollen for Senate instead.

"We had a lot of high hopes; we were hoping she'd do well," said Pat Lippold, the political director of the union. "I think our members have been very disappointed."

The union chose to disclose its role in creating the super PAC days ahead of a filing deadline with the Federal Election Commission in which documents might have made that connection plain anyway.

Lippold said 1199SEIU never intended to hide its involvement. Super PACs may receive unlimited funding but are barred from coordinating their efforts with the campaigns.

The 1199SEIU super PAC uses an analysis by InsideGov.com to call Edwards ineffective. It begins with a montage of people.

"Because protecting them takes more than good intentions, we need a senator who does more than talk," the narrator says in the ad. "Donna Edwards was ranked one of the least effective members of Congress — among Democrats, dead last."

InsideGov.com ranks lawmakers based on how many bills they have drafted that have been approved by a committee, a crude metric given the complexity of how laws are made and the fact that Republicans decide which bills are put to a vote.


An anti-Van Hollen ad, paid for by a super PAC called Working For US, received more attention Tuesday. That spot highlighted a legislative effort by Van Hollen in which critics said he and other Democratic leaders created a carve-out for the National Rifle Association.

Ironically, the underlying bill that Van Hollen was pushing would have required corporations, unions and nonprofits to disclose campaign spending more thoroughly.

Working for US has received money from unions in the past, but its more recent financing is murky and a spokesman for the group declined to detail its recent donors.

The Obama administration and House Democrats, eager to roll back the impact of the Supreme Court's decision in Citizens United in 2010, were attempting to press the disclosure bill through Congress. In an effort to bring more Democrats on board, House leaders included an exemption for the gun lobby. They later tweaked the bill to exempt a broader array of groups, and it passed with all but 36 Democrats.

Edwards voted against the measure; Van Hollen supported it.

"The NRA and its campaign cash is what stands between us and gun reform," the ad's narrator says. "Chris Van Hollen met with NRA lobbyists to craft a loophole that would let the NRA skirt a new campaign finance law."

The ad includes a video of President Barack Obama speaking about the deaths at the Sandy Hook massacre in 2012 — subtly suggesting the president opposed the bill. In fact, the opposite is true: Both the White House and some liberal Democrats, including Rep. Elijah E. Cummings of Baltimore and then-House Speaker Nancy Pelosi, supported it.

Hoyer called the ad "dishonest" and "shameful."

"The ad released today by the Working for US PAC is dishonest and should be taken down," Hoyer said in a statement. "The bill had nothing to do with gun violence. ... Chris's record is clear, and this attack ad, which tries to imply otherwise, is shameful."

The anti-Van Hollen ad is running on broadcast television in both Washington and Baltimore, and also on cable television. The group's donors are expected to be disclosed later this week in an FEC filing.

A spokesman for the group defended the ad.

"There's the D.C. insider way of getting things done — which too often means watered-down compromises and shoddy deal-making at any cost," said Joshua Henne, a spokesman for the group. "And then are leaders like Donna Edwards ... she isn't someone who trades her strong principles to cut bad deals."