New Britain — From the opening seconds of a U.S. Senate debate carried live on public radio today, Susan Bysiewicz cast U.S. Rep. Chris Murphy as beholden to Wall Street and a contributor to the dysfunction in Congress.

It’s been a hard sell. Her line of attack is contradicted by left-leaning corporate critics like the Working Families Party and, more recently, the Connecticut Citizen Action Group as they have joined establishment Democrats in lining up behind Murphy.

“Susan has been using this tired line of attack for the last year and a half, and it hasn’t worked,” said Murphy, who adopted the dismissive tone of a frontrunner in responding to most of Bysiewicz’s attacks.

But Bysiewicz signaled again today it remains her strategy against the 38-year-old Murphy, who was elected to Congress in 2006 by unseating the senior member of the Connecticut delegation, Republican Nancy Johnson.

“Since becoming a member of Congress, Chris Murphy has accepted more than $1.5 million from Wall Street,” said Bysiewicz, who was secretary of the state for 12 years ending in 2011.

The debate at Central Connecticut State University was moderated by John Dankosky of WNPR, with questions posed by a CCSU faculty member who set in motion the events leading up to this year’s open seat: Ned Lamont.

It was Lamont’s victory in the 2006 Democratic primary that forced Sen. Joseph I. Lieberman to seek re-election that year as an independent. Lieberman won in 2006, but as an independent he had a diminished political base had he run in 2012.

Bysiewicz has been in search of what Lamont enjoyed in 2006: a galvanizing issue like the war in Iraq that energized his candidacy, drawing grass-roots activists like Tom Swan, the CCAG executive director who ran Lamont’s campaign.

On Wednesday, it was Swan who announced CCAG’s endorsement of Murphy.

“Chris has a tremendous track record of standing up to moneyed interests to make government work more effectively for Connecticut families,” Swan said. “His election will be the type of change Connecticut voters need and deserve in the US Senate.”

The dynamic of the race was evident in the debate: Murphy is the front-runner for the Democratic nomination, endorsed by the party’s convention, nearly every prominent office holder, unions and other grass-roots groups.

There is no obvious wedge issue dividing Murphy and Bysiewicz. On key issues they agree, although the draft unexpectedly emerged as a dividing line.

The other panelist, Oz Griebel, a Republican business leader who ran for governor in 2010, asked the candidates their thoughts about mandatory public service, including a possible re-imposition of the military draft.

Bysiewicz left open the possibility of a supporting a new draft, saying that World War II and Korean veterans she recognized as secretary of the state told her that a draft led to a diverse military and a nation vested in the military in ways it is not today with an all-volunteer armed services.

“I don’t support the re-imposition of the draft,” Murphy said. “The draft doesn’t make sense to me.”

Whenever possible over the 90-minute debate, which will be rebroadcast tonight at 7 p.m., Bysiewicz returned to casting Murphy as responsible for a dysfunctional Washington and a tax structure that favors the rich.

“We’re in the economic mess we’re in because Wall Street is way too cozy with Washington,” she said. “We need to reform Congress if we want to hold Wall Street accountable and rebuild the middle class.”

As she has since their first debate in March, Bysiewicz raised Murphy’s vote in 2010 against a bill whose provisions would have closed the so-called “carried interest” tax break for hedge fund managers.

Murphy said he has voted to close the loophole in other bills, but he objected to that bill because it would have increased the deficit by $50 billion.

“That’s why I voted against it,” he said.

Bysiewicz  cited the recent $2 billion trading loss by J.P. Morgan and asked Murphy if he would return a $6,000 contribution from the investment house’s political action committee.

Murphy ignored the question and addressed the larger suggestion: He was too cozy with Wall Street. He touted his vote for financial reforms, saying, “The Wall Street bankers hate the Wall Street reform bill.”

Bysiewicz has found the religion of Wall Street reform late in her career, and she has taken her own contributions from financial services companies, he said.

“She doesn’t seem to have a problem with those,” he said.

Bysiewicz replied, “You’ve taken hundreds of thousands of dollars from all the bad actors in the banking crisis.”

Two-third into the debate, Bysiewicz made her first overt appeal to women, an important constituency in Democratic primaries. She mentioned the Blunt Amendment, which would allow private employers to deny coverage for contraceptives if they are morally opposed.

“We very desperately need to have more women in the U.S. Senate and Congress so that we don’t have to keep re-litigating debates we had 50 years ago about access to contraception and reproductive health care,” Bysiewicz said.

Linda McMahon, who is competing with Chris Shays for the Republican nomination, frequently says it is time for Connecticut to elect a woman.

Bysiewicz returned to the theme in the debate’s last minute, when she attacked McMahon and the programming of the company she co-founded, World Wrestling Entertainment.

“I’ll be darned if I let someone who sells and violence and pornography for a living be our next United States senator,” she said. “We need to send the right woman to Washington.”