MADISON, Wis. -

A Guardian US report released Wednesday details previously undisclosed donations made by the lead paint industry to groups supporting the re-election of Republicans in Wisconsin.

Leaked files provided to Guardian reporters reveal that the owner of NL Industries, a leading producer of lead that was added to paint before it was banned, donated $750,000 to the Wisconsin Club for Growth during campaigns for Senate recalls in 2011 and 2012.  The owner, Harold Simmons, died a year after Walker won his recall election, according to the report.

The article also says that in that same time frame and after the donations, senators passed and Gov. Scott Walker signed legal changes that would have allowed immunity to lead manufacturers from civil cases related to lead poisoning.

Details show that senior campaign adviser to the governor, Keith Gilkes, sent information to the governor about Simmons as a possible donor and issues in his past, including lead poisoning cases in Milwaukee.

A spokesman for the governor's campaign has been pushing back on the issue since the story was released.

"As widely reported two years ago, the prosecutor’s attorney stated that Gov. Walker was not a target," said campaign spokesman Joe Fadness. "Several courts shut down the baseless investigation on multiple occasions, and there is absolutely no evidence of any wrongdoing."