Reporter Nikita Stewart explains Jeffrey Thompson's significance in D.C. politics and connections to key figures. (The Washington Post)

The D.C. businessman at the center of an ongoing city corruption investigation secretly spent more than a half-million dollars on get-out-the-vote efforts for Hillary Rodham Clinton’s 2008 presidential campaign, according to interviews and court documents filed Wednesday.

Jeffrey E. Thompson, a former city contractor who allegedly financed a secret campaign for then-mayoral candidate Vincent C. Gray (D) in 2010, financed an independent effort to reach urban voters on behalf of Clinton in Texas and at least three other states during the 2008 Democratic primaries, according to the interviews and documents.

Thompson allegedly paid Troy White, a New York marketing executive, more than $608,000 to hire “street teams” to distribute posters, stickers and yard signs beginning in February 2008 to help raise Clinton’s profile during her primary battle with then-Sen. Barack Obama, according to the documents and interviews with several people familiar with the investigation.

A search of federal campaign records found no evidence that Thompson or White disclosed the alleged expenditures or activities to the Federal Election Commission, as required by campaign finance laws.

The new accusations came to light when White pleaded guilty Wednesday to a misdemeanor tax charge, becoming the latest Thompson associate implicated in a far-reaching investigation that has explored the businessman’s alleged secret role in funding political campaigns.

For the first time, the investigation has connected Thompson to a major national political figure. The investigation could have implications for Clinton, who is weighing a second run for president in 2016 and is seen as an overwhelming favorite for the Democratic nomination.

Thompson’s attorney, Brendan Sullivan, declined to comment.

An attorney for Clinton’s 2008 campaign, Lyn Utrecht, said in a statement late Wednesday that the campaign “has cooperated fully” in the White case.

A senior official on Clinton’s 2008 campaign said no one in the campaign’s senior leadership or with budget-making authority knew about White’s independent canvassing campaign. Other senior officials said they had never heard of White.

“I’m absolutely certain he had nothing to do with any of us,” said Garry Mauro, chairman of Clinton’s Texas campaign. “I was at the headquarters almost every day, I traveled the state, and I never heard of this guy.”

The allegations that Thompson secretly helped Clinton in Texas and at least three other primary states in 2008 are similar to allegations about activities surrounding the Gray campaign. Two of those states were North Carolina and Indiana, according to people familiar with the case. The fourth state was unknown.

Prosecutors have been building a case against Thompson, who has been described in court documents as the financier of a secret campaign for Gray’s successful run for mayor, and court records show that he is the subject of a grand jury investigation.

Neither Thompson nor Gray has been charged, and the mayor has denied any wrongdoing. Thompson has not been named in any of the documents, but several people with knowledge of the case have identified him as the businessman in those documents.

White admitted to failing to file corporate income tax returns for fiscal years 2007 through 2010 that would have reflected the alleged indirect payments from Thompson. He faces up to 12 months in prison, according to federal sentencing guidelines.

White, a 48-year-old Howard University graduate based in New York, provides marketing services, including services to political campaigns, through his firm Wytehouse Marketing. His services include managing what he calls “street teams,” which one person familiar with White’s services said includes distributing leaflets at nightclubs, shrink-wrapping vehicles with campaign images and messages, and other grass-roots canvassing, often related to urban pop culture.

Court documents and interviews indicate that in early 2008, as Clinton struggled to make up ground against Obama in the primaries, White directly approached the Clinton campaign, pitching his ability to help organize supporters in urban areas. After campaign officials declined his services, a longtime Clinton adviser, Minyon Moore, helped connect White with Thompson, who agreed to fund his canvassing operation, according to the documents and interviews.

Utrecht, the Clinton campaign attorney, emphasized in her statement that the campaign “turned down Mr. White’s services.”

Moore is not identified in the documents, but several people with knowledge of the case said she is the campaign official described in those documents.

Moore, who began her career in Chicago as an organizer for Jesse Jackson’s 1988 presidential campaign and for Jackson’s Rainbow PUSH Coalition, became one of the Clintons’ closest political advisers. She served as director of political affairs in the Clinton White House and later as chief executive of the Democratic National Committee.

On Hillary Clinton’s 2008 campaign, Moore was a senior adviser, working closely with many departments of the campaign, and she was particularly instrumental in African American outreach. She was one of the District’s 21 “superdelegates.”

Moore now works at Dewey Square Group, a Washington-based consulting firm, where she heads the multicultural and state and local affairs practices.

The court documents quote from e-mails detailing the conversations. A person described as a senior campaign official told White, “Unfortunately, we are not going to be able to use the street teams.” The person described himself or herself as a “big fan” and expressed a hope that “we can work together soon.”

People close to the case who were not authorized to speak publicly about it said the senior official is Guy Cecil, who served as Clinton’s national political and field director. Cecil, now executive director of the Democratic Senatorial Campaign Committee, declined to comment.

Two days later, White followed up with Cecil and Moore, according to the documents.

According to the documents, Moore wrote back to White and Cecil: “I am piping up saying we need your services.” Moore told Cecil in the same message, “Let’s [find] some money. I will fight for it.”

Soon after, Moore introduced White to Thompson, according to the documents. White put together a get-out-the-vote plan in advance of the March 4 Texas primary and caucuses, and Thompson agreed to cover the costs.

In a statement late Wednesday, Dewey Square Group said Moore has been “fully cooperating” with the federal investigation. “The facts make clear that she was entirely unaware of any inappropriate activities and at all times conducted herself, as she always has, not only in full compliance with the law but in accordance with the highest ethical and professional standards.”

Spending in support of candidates must be reported by individuals funding independent expenditures — not by the candidate’s committee. The law also prohibits independent committees from coordinating directly with political campaigns or parties.

According to prosecutors, White maintained contact with Moore, who arranged for Clinton’s Texas campaign office to provide White’s “street team workers” with campaign-prepared materials — such as bumper stickers and yard signs. Moore also gave White “confidential internal information” about the campaign’s itinerary, according to the court filing.

“The paid street team workers and canvassers then were directed to attend these campaign events to show support for [Clinton] and disseminate and distribute [Clinton's] prepared materials,” according to the document signed by White.

U.S. District Judge Colleen Kollar-Kotelly asked White during the hearing whether there was “some cooperation” between the official campaign and his operation. White responded, “Yes.”

White’s attorney, Ross Nabatoff, declined to comment after the hearing.

Thompson has a long history of supporting Bill and Hillary Clinton, making donations to their political campaigns as well as to the family’s charitable foundation. According to campaign finance records, Thompson, his associates and his companies gave $65,500 to Hillary Clinton’s 2008 campaign, as well as a total of $11,950 to Obama’s 2008 and 2012 campaigns.

In financing the White’s canvassing operation, Thompson allegedly funneled money from two of his companies through a third business, Belle International, owned by Jeanne Clarke Harris, his longtime associate, according to the documents.

Harris, a public relations consultant, pleaded guilty last year to participating in the alleged off-the-books campaign for Gray by funneling Thompson’s money through companies she owned.

White lists both Hillary Clinton and Obama as political clients.

Alice Crites, Mike DeBonis and Nikita Stewart contributed to this report.