MADISON, Wis. — Lost in the hoopla over the effort to recall Wisconsin Gov. Scott Walker after he took on union rights is an ongoing secret investigation that has already ensnared a handful of the Republican governor’s former aides.

The investigation by Milwaukee County’s district attorney hasn’t resonated with voters, but with the June 5 recall less than three weeks away Democrats have started playing up questions about why Walker created a criminal defense fund for himself and whether the governor might face charges next.

Walker has branded the strategy a “cheap political stunt,” but Democrats are banking that the tactic will help them curry favor with the dwindling pool of undecided voters who could turn the election.

“The public deserves some answers as they try to decide who to vote for,” said Jeremy Levinson, an attorney for the state Democratic Party.

Republicans say Democrats are grasping for an edge as polls show Walker pulling ahead of Milwaukee Mayor Tom Barrett. The most recent Marquette University Law School poll, released Wednesday, showed Walker leading by 6 percentage points after the race was essentially a dead heat a month ago.

“When you’re down or your message isn’t playing the way you want it to in a tight race, you’ve got to find something else,” said Brandon Scholz, a Madison lobbyist who has worked on a number of GOP congressional races across the country.

The push to recall Walker began last year after he championed a contentious law stripping most public sector workers of nearly all their collective bargaining rights. Democrats called it an all-out attack on organized labor, but Barrett’s easy primary victory over an opponent backed by most of the state’s major unions signaled the momentum for the collective bargaining argument may have started to fade.

Barrett moved on to beating up Walker over his inability to create jobs, harping on a U.S. Bureau of Labor Statistics report that found Wisconsin lost the most jobs of any state between March 2011 and March 2012.

Meanwhile, Milwaukee County District Attorney John Chisholm has been quietly investigating Walker’s associates during the governor’s tenure as Milwaukee County executive. Chisholm, a Democrat, has set the probe up as a so-called John Doe proceeding, meaning his prosecutors can subpoena witnesses and compel them to testify while barring them from speaking publicly about the case. Five people have been charged so far on allegations ranging from embezzling money from a veterans trust fund to campaigning on county time.