Rep. Chris Van Hollen (D-Md.) out-raised House colleague and Senate primary rival Rep. Donna F. Edwards for the second quarter in a row. (Right: J. Scott Applewhite/AP. Left: Melina Mara/The Washington Post)

Rep. Chris Van Hollen maintained a nearly 3-to-1 fundraising advantage against Rep. Donna F. Edwards, his Democratic primary rival in the Maryland race to replace retiring U.S. Sen. Barbara Mikulski (D), according to second-quarter numbers provided by the two campaigns.

Van Hollen improved on his first-quarter total, raising $1.5 million in contributions between April and June and bringing his overall haul to more than $2.6 million since January, according to his campaign and federal data. His spokesman said Van Hollen has $3.5 million in cash on hand.

Edwards’s campaign said the congresswoman also did better in the second quarter, raising $590,000 between April and June to increase her year-to-date fundraising to $924,000.

The candidates must file a more detailed account of their finances with the Federal Election Commission by Wednesday.

Rep. Chris Van Hollen (D-Md.) represents Maryland's 8th Congressional District . (Jahi Chikwendiu/THE WASHINGTON POST)

Both campaigns are eager to bolster their standing with progressive voters, and both claim to have tapped into a “low-dollar” grass-roots donor base for a large portion of their contributions.

Van Hollen said more than 75 percent of his donations have come from Maryland — a direct jab at Edwards, who draws more of her support from national progressive groups.

Van Hollen also has touted his support in Edwards’s home base of Prince George’s County, where he has received endorsements from politicians including state Sen. Joanne C. Benson (D-Prince George’s) and Prince George’s County Executive Rushern L. Baker III (D).

Edwards, who was endorsed by several members of the Prince George’s County Council, defended her fundraising in this cycle, saying she received donations from more than 10,000 contributors who “reflect the progressive momentum” building around her campaign. Edwards did not say how many of those donors are from Maryland.

The four-term congresswoman is not a darling of the state’s political establishment. To win office in 2008, Edwards unseated a popular Democratic incumbent whom she portrayed as being too cozy with business.

Her success was due in part to support from organized labor and large numbers of African American voters, especially women, who turned out to vote for Barack Obama for president.

In the Senate race, Edwards and Van Hollen have split support among organized labor in the region and state. Edwards is backed by one of the largest local chapters of the Teamsters, but the union’s umbrella organization went with Van Hollen.

Rep. Donna F. Edwards (D-Md.) is running against Van Hollen in the primary race for Sen. Barbara Mikulski’s seat. (Jeffrey MacMillan/For The Washington Post)