Opening a new line of attack in the contentious Democratic primary in Maryland’s 6th Congressional District, State Sen. Rob Garagiola sent an e-mail to supporters Wednesday noting that his opponent, John Delaney, had made a political contribution to Republican Andy Harris in 2010.

The e-mail includes a link to a Federal  Election Commission report documenting the $2,400 donation, which was made a week before the midterm election. Harris ultimately won the election by a large margin, beating incumbent Democrat Frank Kratovil in a race that helped swing control of the House to the GOP.

“Many of you answered the call in that race by writing a check, going to the Eastern Shore, knocking doors, and volunteering as needed,” Garagiola writes in the e-mail. “I personally knocked on doors.  While I was knocking on doors for Frank, Delaney was writing Andy Harris a check.”

In a statement, Delaney campaign manager Max Cummings noted the hundreds of thousands of dollars Delaney has raised or contributed directly to Democrats over the past several years. Cummings said it was Garagiola who had sided with Republicans in the past, including in his work as a lobbyist. The statement does not address the Harris contribution directly.

“The real tragedy here is that instead of attacking a life-long Democrat who has helped dozens of Democrats get elected, Garagiola should have come clean about his own Republican ties,” the statement read. “It is undisputable that John Delaney has been one of the strongest, most committed Democratic Party supporters, and it is a shame that Rob Garagiola resorts to such desperate attacks.” 

Delaney, a Potomac banker, and his wife have been prolific givers to the Democratic party for years. In 2008, the couple contributed nearly $50,000 to the Democratic National Committee. He has given to a broad range of Democrats, including Barack Obama, Hillary Clinton, Senate Majority Leader Harry Reid and former congressman Rahm Emanuel, the current mayor of Chicago.

The donation to Harris appears to be the only one Delaney has made to a GOP candidate in recent years. 

But the Garagiola campaign is likely to beat hard on that donation, particularly since the 2010 race has parallels to the 6th District race this year, with both capturing significant national attention. The campaign made the donation public on several fronts, including on Twitter and in a web video.

The race has turned negative, with Garagiola accusing Delaney of using his wealth to buy the seat – campaign finance reports show Delaney wrote his campaign a $118,000 check last year – and Delaney accusing Garagiola of being a career politician who has accepted campaign checks from special interests with business in Annapolis.

The primary is set for April 3.