Kathleen Matthews, right, a Democrat in Maryland’s 8th Congressional District race, greets supporters after a forum last year in Rockville. (Evelyn Hockstein for The Washington Post)

Maryland congressional candidate Kathleen Matthews has put $500,000 of her own money into her 8th District Democratic primary race, according to new campaign spending reports filed with the Federal Election Commission.

Matthews’s disclosure only swells the river of cash that has made the primary one of the most expensive House races in the country, with total fundraising topping $15 million.

The former WJLA anchor and Marriott executive was presumed to have the financial upper hand before Potomac wine retailer David Trone entered the race, just before the Feb. 3 filing deadline. Trone has vowed to spend as much of his personal fortune as it takes to win the April 26 primary. Filings show that he has contributed just under $10 million and has almost $950,000cash on hand.

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Matthews — whose new TV ad has her expressing confidence that Maryland voters “will reject the notion that congressional seats can be purchased like an expensive bottle of wine” — said in a statement that she owed it to her supporters to try to remain competitive.

“We’ve been incredibly successful, but when one of our opponents decided to spend record-breaking amounts, I believed I had a responsibility to my generous supporters to ensure we had the resources­ to run a winning campaign,” Matthews said.

The $500,000 personal contribution — made in two $250,000 segments March 17 and April 4 — matches the half-million dollars she raised in the first quarter of 2016. She has collected $2 million since beginning her campaign in the summer. Matthews had $424,000 cash on hand as of April 6.

She is also underwritten by $250,000 in independent expenditures on her behalf from a super PAC aligned with Emily’s List. The group, which works to elect Democratic women who support abortion rights, has spent $200,000 on mailings for Matthews.

She was outraised in the first quarter by her other principal opponent, state Sen. Jamie B. Raskin (Montgomery), who collected just under $561,000, giving him a total of $1.8 million for the 2015-2016 cycle. Raskin has $624,000 in the bank, according to his new report.

Trone disclosed in a newspaper ad this week that he had spent $9.1 million through early April. His report fills in some of the details.

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The largest share went to GMMB, a Washington political media firm that purchased his television, radio and digital advertising. Trone also spent more than $800,000 for his extensive direct-mail effort.

The report also shows that Trone’s campaign was effectively up and running months before he formally announced his candidacy in late January. Trone’s campaign manager, Kurt Staiger, and other staff were on salary as early as August. Pollster Harrison Hickman and two research-and-consulting firms, inVeritas of Little Rock and Zero Week Solutions of Los Angeles, were also on board last year. Trone’s own contributions in the pre-campaign period came to at least $1.8 million.

Under the FEC’s “Testing the Waters” provisions, prospective candidates are allowed to spend funds but are bound by the same fundraising regulations that are in place during a campaign, with individual donations limited to $5,400. But Trone, who took no outside funds, was free to spend as much as he wanted.

Trone spokesman Andrew Friedson said the campaign hired lawyer Scott Thomas, a former FEC commissioner, “to help him every step of the way to ensure he was complying with both the letter and the spirit” of the law.

The other five Democratic contenders for the seat being vacated by Rep. Chris Van Hollen (D) continued to lag far behind the top tier. Among this group, Will Jawando, a former Obama White House aide, was the top fundraiser for the quarter, reporting $125,596, with cash on hand of $79,041. Former State Department official Joel Rubin collected $105,972 and reported $49,033 in the bank. He has also been supported by a Pittsburgh-based super PAC that spent nearly $40,000 on digital ads and has about $60,000 left. Del. Kumar P. Barve (Montgomery) raised $70,000 and is left with $64,409 cash on hand.

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Del. Ana Sol Gutiérrez (Montgomery) raised just $22,085 in the first quarter but has $167,600 cash on hand from previous fundraising. That includes $94,500 in personal loans she has made to the campaign. Nonprofit executive David M. Anderson raised $10,039 since the first of the year, leaving him with $26,653 in cash. He has also contributed $60,000 in personal loans.

On the Republican side, Silver Spring media consultant Aryeh Shudofsky raised $9,447 in the first quarter and had $7,822 cash on hand. Frederick lawyer Dan Cox collected $8,515 and has $5,373 in the bank.

Silver Spring business consultant Liz Matory and Silver Spring lawyer Shelly Skolnick said Friday that they were still completing their reports. Bethesda pastor Jeffrey W. Jones has not reached the $5,000 fundraising threshold that triggers the requirement to file a report.