Concerned Taxpayers of America, one of the numerous political groups spending big on this year's elections, appears to consist of two taxpayers in particular.

Daniel G. Schuster Inc., an Owings Mills, Md., concrete firm, gave two donations to the group totaling $300,000, new disclosure records show. New York hedge fund executive Robert Mercer gave the group $200,000.

And that's the extent of the financial support reported by Concerned Taxpayers, which says it was formed in September "to engage citizens from every walk of life and political affiliation" in the fight against "runaway spending."

The group's rapid creation - and its narrow funding base - illustrates how one or two wealthy donors can have a dramatic impact on political races, particularly in the wake of recent court rulings that have swept away many traditional spending limits. The situation also underscores how the precise motivations and goals of many independent groups can remain stubbornly opaque, even when disclosure is required.

The Concerned Taxpayers, which lists a Capitol Hill townhouse as its address, has spent $450,000 on television advertising targeting just two lawmakers: Reps. Peter A. DeFazio (D-Ore.) and Frank M. Kratovil Jr. (D-Md.).

When the group began targeting DeFazio several weeks ago, both he and his GOP opponent, tea party favorite Art Robinson, said they were unfamiliar with the group and were surprised by the ads.

The organization is a "super PAC" that can spend and raise unlimited funds, but it is not allowed to coordinate with campaigns and is required to report - eventually - its funders to the Federal Election Commission. That deadline came Friday, when the group turned in reports listing Mercer and the Maryland concrete firm as its only two donors.

Neither Mercer nor Daniel Schuster, the concrete firm's founder, could be reached for comment Saturday. Jason Miller, who is listed as the treasurer of Concerned Taxpayers of America, also could not be reached.

DeFazio said in an interview Saturday that he remains mystified by the group's attacks on him, but noted that he co-sponsored legislation to levy a tax on major hedge-fund transactions. Mercer's firm, Renaissance Technologies, is one of the leading hedge-fund companies on Wall Street and would be dramatically impacted by such a proposal.

"I have been one of the most prominent critics of Wall Street and tried to call them to account," DeFazio said. "I've obviously made some powerful enemies."

Robinson said he is acquainted with Mercer but had no idea he was connected to Concerned Taxpayers. His campaign has received $9,600 in donations from Mercer and his relatives, FEC records show.

"I don't know him very well, but I do know him and I respect him," Robinson said. "If he's helping me in the campaign, then I'm grateful."

In Maryland, Schuster is listed in FEC reports as the top contributor to Kratovil's GOP opponent, Andy Harris. Harris's campaign did not respond to a request for comment.

Jessica Klonsky, Kratovil's campaign manager, said, "It's no surprise that Harris's top campaign contributor is spending hundreds of thousands of dollars to repeat the same misleading attacks that are coming from the Harris campaign itself."

eggend@washpost.com

Staff writer T.W. Farnam contributed to this report.