Momentum is such a hard word to define when it comes to a Congressional campaign.

With less than a week to go before Virginia’s primary elections, the campaigns of both Democratic candidates in the Fairfax County-based 11th district are claiming that the momentum of the race has swung firmly in their favor.

Supporters of former Rep. Leslie Byrne (D) point to her late campaign contribution strength and a recent spat of negative headlines for Fairfax County Board of Supervisors Chairman Gerry Connolly (D) as the reasons why she is surging at this final stage of the campaign.

On Tuesday, Byrne’s campaign kept those headlines in the spotlight by filing a Federal Election Commission complaint against Connolly, accusing him of violating campaign finance rules after a senior government contractor for a firm where Connolly works part time encouraged employees to donate to the candidate in an e-mail solicitation.

But Connolly’s supporters say Byrne is shooting herself in the foot with her negative campaign tactics — and that she’s had to go negative because she knows she’s behind.

The FEC complaint “is last-minute desperation from Leslie Byrne,” Connolly spokesman James Walkinshaw said. “This is just her modus operandi … negative campaigning and false accusations.”

Connolly campaign consultant Tom King said Tuesday that he thinks Byrne’s negative campaign tactics are going to cause a backlash at the ballot box. But while she continues down that path, “Gerry Connolly is working his tail off to get voters out to the polls,” King said.

Polling has been difficult to read over the course of the campaign. Back in January, Byrne released polling claiming she was ahead. Connolly released polling in January and April showing himself with 20-point leads. Just two weeks ago Byrne’s camp released another poll showing her behind, but within the margin of error in the race.

The bottom line is that this race — which also features two second-tier candidates — has tightened considerably in recent weeks, and the only thing everyone seems to agree on is that turnout is going to be very low next Tuesday, perhaps in the low 20,000s.

The winner of the Democratic primary race will go on to face Republican Keith Fimian in the general election, and though the seat has been held since 1995 by retiring Republican Rep. Tom Davis, the Democratic nominee is expected to be favored in the fall. This suburban Washington, D.C., seat has only become more ethnically and racially diverse since President Bush won it by a little more than 2,000 votes in 2004. While Davis remains popular in the district, Fimian, a businessman who has raised considerable money, is not well known.

In the past week, Byrne, who served in Congress for a single term before being defeated by Davis in her first re-election bid in 1994, has been touting her endorsement by a growing number of Congressional colleagues, including Sen. Jim Webb (D-Va.).

Democratic Reps. Corinne Brown (Fla.), Sam Farr (Calif.), Maurice Hinchey (N.Y.), Marcy Kaptur (Ohio), Carolyn Maloney (N.Y.), Nydia Velázquez (N.Y.) and Lynn Woolsey (Calif.) have also offered their endorsements.

“With momentum in her favor after reports that the Democratic primary race in Virginia’s 11th congressional district is a dead heat, Leslie Byrne announced today that she has now been endorsed by eight sitting members of Congress,” a Byrne news release said earlier this week.

Last week, her campaign was quick to tout her financial gains on Connolly, who, earlier this year, was expected by many pundits to soundly win the fundraising battle — and the primary.

A Byrne campaign release stated that “despite Gerry Connolly’s close ties to wealthy developers and corporate interests,” Byrne had more cash on hand than Connolly during the latest fundraising period, from April 1 to May 21, and raised more money during that time, according to Federal Election Commission reports.

A major portion of Byrne’s fundraising success this spring has to be credited to the fundraising power of the pro-abortion rights group EMILY’s List, which endorsed her in February.

But Connolly’s camp has argued that Byrne is looking in the wrong places if she wants to talk about financial momentum in the race. Connolly raised about $120,000 more than Byrne during the course of the entire campaign through May 21, despite getting into the race months after Byrne. Connolly had also spent $130,000 more than Byrne had through that same time period.

As for Byrne’s list of Congressional endorsements, Walkinshaw said, “Each day she’s announcing a new Member of Congress from California or Connecticut or wherever they are from that are coming out and endorsing her, which is nice, but we’re focusing on the 11th district, and we think we’re doing pretty good here.”

Included on Connolly’s endorsement list is Virginia Gov. Tim Kaine and former Virginia Rep. Herb Harris (D).