With the threat of a perhaps the worst presidential candidate in history actually getting elected looming, groups are doing everything they can to stop Donald Trump’s rise.

According to The New York Times, an anti-tax super PAC called Club for Growth Action spent $2 million in ads targeting the Republican presidential frontrunner, to air in Illinois ahead of the March 15 primary.

“Everything hinges on March 15,” Doug Sachtleben, a spokesman for Club for Growth, told the Times. “If he were to have a solid day and win Ohio and Florida, it gets very difficult to press forward.”

Last September, Trump threatened to sue the organization, saying that claims that he would raise taxes across the board as president weren’t true.

One of the group’s most high-profile donors is Peter Thiel, co-founder of PayPal and Facebook’s first outside investor.

[Image via Getty]

Contact the author at melissa.cronin@gawker.com.