U.S. Rep. Mazie Hirono and former Congressman Ed Case had strong fundraising performances over the past three months in the Democratic primary campaign for U.S. Senate, according to their campaigns, but Hirono has the early cash advantage.

Hirono and Case stressed the need for early fundraising to potential donors because the figures offer the first objective measurement of the candidates since they announced their campaigns to succeed U.S. Sen. Daniel Akaka, D-Hawaii.

Hirono raised more than $281,000 from April through June, according to a copy of her quarterly report provided by her campaign. The congresswoman had $545,000 in cash on hand, a total that includes more than $100,000 raised during the first quarter of the year and money transferred from her congressional committee.

"I am so proud and humbled by this strong outpouring of grassroots support," Hirono said in a statement. "Close to 200 new donors have joined our campaign within the last few weeks because they want a U.S. senator who’s going to continue the fight to improve our schools, for energy independence, and to get our economy back on track. We know this campaign won’t be easy, so we’re going to keep building a strong grassroots organization throughout Hawaii."

Case said in an email that he raised about $240,000 since he announced his campaign and had about $210,000 in cash on hand. He said his quarterly report was not completed. The reports are due today.

The former congressman predicted fundraising would accelerate in the next quarter as more people, both locally and nationally, focus on the Senate race.

"It is still fluid, with potential candidates of both parties saying they’re still thinking," Case said. "But yes, more folks are viewing it as a stark choice between Mazie and me with the election just a year away and contributing on that basis. As well, folks nationally that have been focused on the marquee Senate races developing are just realizing there’s a major decision in Hawaii that will affect the future of the Senate just as much as any other Senate election nationally.

"I expect a pretty rapid acceleration on all fronts this quarter."

U.S. Rep. Colleen Hanabusa, D-Hawaii, raised $228,000 during the past three months, according to a source familiar with her report. Hanabusa has said she will decide by next month whether to run for Senate. She can transfer the money to a Senate campaign.

Former Gov. Linda Lingle has said she will decide by August whether to enter the Republican primary for the Senate. A Lingle candidacy would increase national attention on the Senate race and put pressure on the Democratic contenders. None of the Democrats has shown the ability to raise as much money as Lingle in previous statewide campaigns.

"Obviously, when you have two guys going head to head, it does set up some dynamics, no question about that," Dante Carpenter, chairman of the Democratic Party of Hawaii, said of a primary between Hirono and Case.

Carpenter said Demo­crats might be holding back their financial or political support until they are sure the field is set. Hanabusa and former Honolulu Mayor Mufi Hannemann have said they might run, and the more crowded the primary, the more competition for donations and endorsements.

"We’re probably talking about a very expensive campaign, so that’s an initial consideration that may be a drawback," he said.