Even as Gov. Scott Walker of Wisconsin looks ahead to 2016 and a possible presidential bid, his political past as Milwaukee County executive has come back to haunt him.

A release of 27,000 emails and hundreds of court documents on Wednesday portrays Mr. Walker, a Republican, as having presided over an office where aides used personal computers and email to conceal that they were mixing government and campaign business. The conduct of campaign work on government time led to the criminal convictions of two aides and several others. Mr. Walker, who has for years denied wrongdoing, was never charged.

The messages showed how actively Mr. Walker’s campaign coordinated with county workers in 2009 and 2010, when he was running for governor. They shared emails about the proper wording of campaign news releases. They exchanged emails on county time promoting a birthday fund-raising event for the campaign.

Some used private email accounts to communicate even, apparently, with Mr. Walker, according to an email from the county’s administrative director, who at one point advised a colleague to do the same, adding imprecisely, “Consider youself now in the ‘inner circle.’ ” And plans for a daily conference call, the newly released emails show, included members from both his campaign for governor and his county executive staff.