The Supreme Court has rejected an appeal to reopen an investigation into whether Wisconsin Gov. Scott Walker's campaign to fend off his ouster from office illegally coordinated with outside conservative groups.
 
The justices on Monday left in place a Wisconsin Supreme Court decision that shut down the probe of the Republican governor. Walker won his recall election in 2012.

A group of prosecutors began an investigation the same year into whether Walker's campaign coordinated with Wisconsin Club for Growth and other conservative groups on advertising during the recall without reporting the groups' contributions.

Those groups challenged the investigation. Conservative-leaning justices who control the Wisconsin Supreme Court halted it last year. They ruled that the groups and the campaign coordinated on ads that did not expressly call for a candidate's election or defeat. The state court said such coordination amounts to free speech and isn't subject to disclosure requirements.

The controversy attracted renewed attention recently when The Guardian newspaper obtained more than 1,000 pages of leaked documents from the investigation. The newspaper reported that a leading manufacturer of lead that was once used in paint was among a host of corporate leaders who donated to a conservative group that helped Walker and Republican legislators fight the recall challenges.