Wisconsin Gov. Scott Walker solicited heavyweight conservative donors such as Home Depot co-founder Ken Langone, hedge fund manager Paul Singer and real estate magnate Donald Trump to give large contributions to an allied tax-exempt group that backed him and other state GOP lawmakers facing recall efforts, according to newly released court documents.

The court filing cites e-mails in which Walker’s aides urged him to ask for six-figure contributions for the Wisconsin Club for Growth and to remind donors that the group could accept corporate money and did not need to publicly report contributions.

The aggressive efforts by the governor and his campaign staff to raise money for the organization, which allegedly served as a de facto arm of his campaign, are the latest details to emerge about a controversial two-year investigation of whether Walker’s campaign illegally coordinated with outside groups.

No charges have been filed in the investigation, which was still underway when a federal judge halted it in May. Walker was not a target at the time it was stopped, according to an attorney representing the special prosecutor overseeing the case. The case is now set to be argued next month before a federal appeals court.

Walker’s campaign on Saturday described the newly released material as an effort to “smear” the governor.

Wisconsin Republican Gov. Scott Walker. (Kamil Krzaczynski/AP)

“As previously reported, the prosecutor’s attorney stated that Governor Walker is not a target, two separate judges have dismissed the allegations, and the Friends of Scott Walker campaign is not a party to the lawsuit in the 7th Circuit,” spokeswoman Alleigh Marré said in a statement.

The investigation has focused uncomfortable scrutiny on Walker, a prospective 2016 presidential candidate, and spotlighted how huge sums flow through politically active groups, unseen by the public.

Much of the case, which began under Wisconsin’s “John Doe” statute, has been kept secret. But the 24-page document released Friday, which the court appears to have erroneously made public, provides a rare look at the frank manner in which political operatives discuss how to tap into big money.

In the fall of 2011, as Walker faced a burgeoning effort to recall him from office, a fundraiser e-mailed him with ideas about how to raise money for a campaign for his defense run by the Wisconsin Club for Growth, according to the newly released filings.

Among her suggestions: “Take Koch’s [sic] money,” a reference to the billionaire industrialists, and “Get on a plane to Vegas and sit down with Sheldon Adelson. Ask for $1m now,” referring to the casino magnate.

The fundraiser also advised: “Corporations. Go heavy after them to give,” and “Create a new c4.”

The latter is a reference to nonprofit groups set up under section of 501(c)(4) of the tax code. Such organizations, which can do a limited amount of campaign activity without revealing their donors, have emerged as major political players in recent years.

In Wisconsin, investigators thought the governor and his aides “conspired” to use one such group, the Wisconsin Club for Growth, as a hub of outside activity to circumvent state campaign finance rules, according to court documents.

The filing quotes from an April 2011 e-mail from one of Walker’s fundraisers to one of his campaign consultants, R.J. Johnson:

“As the Governor discussed . . . he wants all the issue advocacy efforts run thru one group to ensure correct messaging,” the e-mail read. “We had some past problems with multiple groups doing work on ‘behalf’ of Gov. Walker and it caused some issues. . . . The Governor is encouraging all to invest in the Wisconsin Club for Growth.”

Johnson and Deborah Jordahl, political consultants to the governor’s campaign, were at the center of the operation, prosecutors wrote. Johnson was paid by the Wisconsin Club for Growth and Jordahl signed the checks, according to court papers.

Walker helped raise the money the organization used to support him and other GOP lawmakers facing recall efforts, prosecutors wrote.

David Rivkin, a lawyer for the Wisconsin Club for Growth and its executive director, Eric O’Keefe, said there was nothing illegal about Walker’s efforts to support the organization.

“At a time when President Barack Obama and his cabinet members are raising funds for Democratic super PACs like Priorities USA, it is hardly newsworthy — and certainly not a crime — that Governor Walker would encourage support for groups that support his economic policies,” he said in a statement. “The First Amendment guarantees Americans the right to work together to advance their policy goals, with a narrow exception for coordinated spending that’s equivalent to a campaign contribution. But the prosecutors’ ‘evidence’ does not identify a single expenditure by the Wisconsin Club for Growth even relating to Governor Walker’s recall election, much less one coordinated with the Walker campaign.”

The case will turn on the question of whether independent “issue ads” that stop short of calling for the election or defeat of a candidate can be considered expenditures on behalf of a campaign.

Illegal coordination cases are rare, as they are difficult to prove, top election lawyers say. The Wisconsin investigation is being watched as a test case in an election year in which campaigns and outside groups have increasingly pushed up against the boundaries of coordination.