Update, 3:30 p.m.: Areizaga-Soto called us back to explain that he stands by his news releases and campaign mailers that show Favola took campaign contributions from a top Republican donor and a developer, even though the Arlington Board’s self-imposed policy generally prevents members from accepting contributions from developers. “It’s important for Democratic voters to know who’s funding my opponent’s campaign,” he said.

Original post: Del. Bob Brink has endorsed Arlington County Board member Barbara Favola to replace Sen. Mary Margaret Whipple in what has become an increasingly negative Democratic primary in Northern Virginia.

Brink (D-Arlington) said he had intended to stay neutral in the race to replace his close friend but decided this week to weigh in against Favola’s opponent, Jaime Areizaga-Soto, who he blamed for “Karl Rove-style mudslinging.”

“I’m disappointed that my friend Jaime Areizaga-Soto has been persuaded that victory in the primary can be achieved through slick negative campaign mailings,’’ Brink wrote in a statement. “Voters in our region have shown repeatedly that they want their public officials to talk about the issues that touch their daily lives, and that they have little tolerance for Karl Rove-style mudslinging. Any candidate who doesn’t understand that is unqualified to represent us.”

Areizaga-Soto formerly worked for the general counsel’s office at the U.S. Agency for International Development. His campaign did not immediately return a call for comment Friday.

Brink said Favola “has shown how to translate values into action, and I am certain she will be an effective voice for Northern Virginia’s priorities in Richmond.”

Republicans are in a fierce battle to take control of the Senate, where Democrats hold a fragile 22 to 18 majority. But the 31st District, which includes parts of Arlington, Fairfax and Loudoun counties, is reliably Democratic and the August primary will probably determine the winner in November.

This post has been updated since it was first published.