MADISON, Wis. (AP) — A federal appeals court unsealed documents this week showing that prosecutors believe Wisconsin Gov. Scott Walker illegally coordinated campaign fundraising activities between conservative groups in 2011 and 2012.

No charges have been filed against the governor, who is seen as a potential 2016 presidential candidate. Prosecutors have been investigating Walker and the groups for nearly two years in a proceeding similar to a grand jury probe.

A federal judge temporarily halted the investigation in May, ruling that coordination between the groups isn't illegal under Wisconsin law because they did not engage in true advocacy. Prosecutors have appealed.

Some frequently asked questions and answers about the case:

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WHAT IS WALKER ACCUSED OF DOING?

Prosecutors allege Walker coordinated fundraising efforts between his campaign and a number of conservative groups, including the Wisconsin Club For Growth, Citizens for a Strong America and Wisconsin Manufacturers and Commerce. Those efforts came during recall drives against him and Republican state senators in 2011 and 2012. Democrats launched the recall drive in retaliation for Walker's passage of a law that stripped most public workers of nearly all their union rights.

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WHY DO PROSECUTORS SAY THAT'S ILLEGAL UNDER STATE LAW?

Prosecutors contend the conservative groups' fundraising and spending in the recalls amount to in-kind campaign contributions that should have been reported to the state Government Accountability Board.

Under state law, they argue, coordination between independent groups and campaigns results in the groups being considered campaign subcommittees, requiring the candidate to report their contributions and spending.

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WHAT HAVE THE COURTS SAID?

Reserve state Judge Gregory Peterson, who was overseeing the investigation, rejected the prosecutors' arguments in January. He wrote that state law prohibits coordination by candidates and independent organizations for political purposes, if those purposes express advocacy — the term in political circles for messages that clearly seek a candidate's election or defeat. But prosecutors didn't show any such advocacy in the groups' activities, Peterson wrote.

U.S. District Judge Rudolph Randa essentially agreed in May when he put a temporary stop to the investigation. He ruled that prosecutors have incorrectly interpreted state law to require that groups report spending on issue advocacy, which is broader and not directed at a particular candidate. Issue advocacy is protected by the First Amendment's free speech guarantee and isn't subject to regulation, Randa said.

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HOW DOES WISCONSIN CAMPAIGN FINANCE LAW COMPARE WITH FEDERAL LAW?

Wisconsin law states that if an individual other than a candidate or a group that's not organized primarily for political purposes spends money on an election, the spending must be reported if it expressly advocates for a candidate's election or defeat. The state Government Accountability Office has issued an opinion stating any coordinated spending must be reported.

Under federal law, whenever an individual or political committee pays for a message that is coordinated with a candidate or a party committee, that refers to a candidate and is delivered shortly before an election, the message is subject to federal reporting requirements. Corporations and labor organizations are barred from coordinating those messages with candidates or party committees.

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WOULD WALKER'S ACTIONS BE ILLEGAL UNDER FEDERAL LAW?

The Walker probe is a state case governed by Wisconsin law, and the two sides are arguing about whether his actions here were illegal. However, coordination with corporations such as the Wisconsin Club for Growth during a presidential run would probably be illegal since corporations and labor organizations can't consult with candidates or party committees on messages, said Brendan Fischer, an attorney for the Center for Media and Democracy, a Madison-based investigative research and watchdog group that focuses on the influence of corporations and other groups on public policy.