MADISON — (CNN) Wisconsin Gov. Scott Walker dodged a major bullet on Thursday, when his home state’s high court killed an investigation that could have led to criminal charges for the newly minted presidential candidate.

A group of Wisconsin prosecutors was looking into whether Walker broke state law in his 2012 recall battle by urging major donors to support his campaign by giving to outside groups without crucial donation limits he faced.

But Wisconsin’s Supreme Court ruled 4-2 Thursday that the investigation was “overly broad” and infringed on First Amendment rights of free speech. The court’s justices, who are elected every 10 years in statewide elections, split over the effect of a pair of recent federal rulings which opened the floodgates for money in federal campaigns.

“We said all along that the courts would ultimately rule on the side of the original circuit court judge,” Walker said Thursday, during a campaign stop in New Hampshire. “As folks in Wisconsin will tell you, I’ve gone through these battles so many times I don’t get up or too down, I’m pretty even keeled on all this.”

But liberal watchdog groups, including many who have hounded Walker throughout his tenure, pointed out that the four justices who ruled in favor of Walker and the outside groups supporting him also received $10 million in campaign themselves from those same groups.

Scot Ross, executive director of the liberal One Wisconsin Now, said that the conflict of interest among the justices was part of a system “run amok”.

“If this exact scenario were occurring in another country, Scott Walker would be calling for boots on the ground to save democracy,” Ross said in a statement.

Prosecutors alleged Walker worked around campaign finance laws to urge donors to give money to give directly to Wisconsin Club for Growth, skirting campaign donation limits in his pricey 2012 recall battle.

But Walker’s lawyers argued in recently unsealed court documents that Walker was not technically a candidate until April 9, 2012, and therefore did not break any state election laws.

The investigation is the second “John Doe” review of Walker’s activities.

The first, launched by Milwaukee County’s Democratic Prosecutor John Chisholm resulted in the criminal convictions of six of Walker’s top aides from his time as Milwaukee County executive.

But the most recent investigation, launched by a bipartisan group of prosecutors and led by a Republican special prosecutor, has been stalled in court.

The term “John Doe” is used to describe the secret investigations local prosecutors can launch, with approval from a judge, under Wisconsin law dating back to its time as a territory.

Walker has made his successful stand against public employee unions central to his argument that he is “unintimidated” in his fight for conservative priorities. He has called the most recent investigation a “political witch hunt.”

The second-term governor is on a national campaign swing this week, stopping through New Hampshire Thursday, before heading on a weekend-long RV tour of Iowa.

The quashing of the investigation is good news for Walker’s most important donors, too. Some details of their internal deliberations were already outed in a Supreme Court filing unsealed this past May, but many more deliberations were threatened to exposure if the investigation continued.

The-CNN-Wire ™ & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved.