With just more than a month until primary Election Day, Democrats trying to dethrone U.S. Sen. Richard Burr may have found the incumbent Republican’s weak spotand unveiled one of their own.

Nationwide, Burr is the most vulnerable Republican senator in the 2010 election, according to Public Policy Polling, a Raleigh-based political analysis firm. Burr, who is finishing his first term in the Senatehe served five terms in the U.S. Househas just a 35 percent approval rating. 37 percent of North Carolinians surveyed disapprove of Burr.

However, the same survey found that Burr would still retain his seat if the election were held today because Democratic candidates lack name recognition and unlike two years ago, Barack Obama won’t be on the ticket to propel party members to victory.

“There are 100 North Carolina Democrats who could have been the nominee and won two years ago,” PPP Director Tom Jensen said of U.S. Sen. Kay Hagan’s win against Elizabeth Dole. “If Obama continues to have a negative net approval, it’s going to be very hard for any of these folks to win.”

But, Jensen says, if Obama’s numbers improve, Secretary of State Elaine Marshall, former state Sen. Cal Cunningham and Durham-based lawyer Ken Lewis, all have a legitimate chance of making Burr’s first term his last.

Marcus Williams of Lumberton, Ann Worthy of Gastonia and Susan Harris of Old Fort are also Senate candidates, but they are running low-key campaigns. The Indy could not reach Worthy or Harris for this story.

Twenty-eight percent of N.C. voters polled have no opinion on the incumbent, despite his lengthy tenure in the U.S. House before beating Erskine Bowles in the 2004 Senate race. That gives Democrats an opportunity to define his service for voters, and makes Burr “really the only option for (the Democratic Senatorial Campaign Committee) to beat a Republican incumbent,” Jensen said.

So far, the hopefuls are running almost in anonymity, especially outside of political insider circles. Among voters, 71 percent have no opinion of Marshall, compared to 85 percent for Lewis and 86 percent for Cunningham, according to the PPP poll.

Elon University Poll Director Hunter Bacot said the Democrats’ campaigns have been low-profile. “Chiding them for not being very public in their campaign would be wrong because they are all pretty much aligned on the issues. There’s not much difference between the candidates besides race and gender,” he said.

And ask the candidates to distinguish themselves from their competitors, they’re vague on their policy differences. However, the candidates are emphasizing their experience and life skills, which they say perfectly positions them to lead in this defining moment.

Marshall talks about defeating NASCAR legend Richard Petty in the 1996 contest for N.C. Secretary of State, becoming the first North Carolina woman to win statewide office. She says she’s helped the state transition to the new economy, attracting business and recouping $340 million in fraudulent securities transitions last year.

“Clearly I have a record of taking on everyone from crooks to Wall Street bankers to get resolutions to valued parties,” Marshall said from the road, between campaign events in Raleigh and Fayetteville.

Cunningham, an attorney and former state senator, touts his military service in the Army Reserves. While serving in Iraq, he was a member of the Judge Advocate General Corps. He earned a Bronze Star for prosecuting defense contractors for misconduct.

“The image of a Democrat in an army combat uniform with a rifle in a combat zone is going to, we think, slow down those who will otherwise just pull the other ticket,” he said.

Lewis reflects on his improbable journey from being the grandson of a slave, to a Harvard Law graduate who left a lofty law firm to start his own practice and help aspiring entrepreneurs.

“I go to Washington with a kind of business experience that is rare among senators,” he said.

What you won’t hear is much about health care, the deficit, jobs or energy. It’s difficult to debate when everyone agrees. In fact, Cunningham says he refuses to campaign against Marshall.

Instead this race is focused on fundraising and heightening the candidates’ profiles by slamming Burr for his conservative stances, particularly on health care.

“The way you show yourself to be a legitimate partisan these days in either party is to be the most vocal and cutting critic of your opponents,” said N.C. State professor Andrew Taylor, chairman of the political science department.

With arrows aimed at the same target, how can voters distinguish the candidates from one another?

Perhaps the most in-depth discussions came at Jane Brown’s Salon, a group of about 20 progressive professors and political activists that began in 1992 as “Rock and Roll Families for Bill and Al.”

Brown, a UNC journalism professor, and her husband, James Protzman of the BlueNC blog, hosted the three Democrats in their Chapel Hill living room for two hours each. The candidates faced a buzz saw of pointed questions from experts on energy, the economy, telecommunications and election politics.

How’d they do? Opinion is split.

George Entenman, a member of the N.C. Democratic Party State Executive Committee, supports Lewis because he displayed the best character, he said.

“I’m sort of giving up on trying to vote for most electable one,” he said. “I decided to go with my feelings in the primary, and after that I’ll go with whoever wins.”

Jan Allen, a former chairwoman of the Orange County Democratic Party, is pushing for Marshall “simply because I think her experience is so vast.”

Tom Henkel, a retired physics professor and energy consultant, is convinced that Cunningham’s appeal for military families makes him the most likely to beat Burr.

None of them could identify any policy differences, though.

“They’re good Democrats. They’ve got basically the same platform at this point,” Henkel said. “The voters have to decide who can beat Burr.”

Marshall says she can do it by carrying the female vote. Lewis says he has gained a boost from Obama supporters. Cunningham believes he can earn Republican votes with his military record.

But they can’t do it without money.

“I hate to say it because it’s a cynical view of politics, but nothing that’s going on right now matters except for the fundraising,” Jensen said.

According to the most recent Federal Election Commission reports filed in December, Marshall has raised $233,000, Cunningham, $320,000 and Lewis, $327,000. All are dwarfed by Burr’s $4.2 million campaign purse. The next reports are due April 15.

UNC professor Leroy Towns, who teaches political communication and spent two decades working on Capitol Hill, says his class can’t understand why no one has separated themselves yet with advertising.

“It seems to me that that Democratic primary was sort of an opportunity waiting to happen, and so far it hasn’t happened,” he said. “Whether it will, I don’t know.”