Hit them where they least expect it.

The Koch-backed Concerned Veterans for America came out with a digital ad last week hitting U.S. Rep. Tim Walz on … veterans issues.

Walz, a DFL candidate for governor, is the ranking Democrat on the House Veterans Affairs Committee and has made care for veterans a defining issue after a 24-year career in the Army National Guard.

Hitting him on veterans issues is a classic Karl Rove move to attack your opponent’s strength, mimicked by the Obama campaign and allies’ ads on Mitt Romney’s business record.

Softening up an opponent this far out is what we’ve come to expect from DFL-aligned groups like Alliance for a Better Minnesota, and it’s a good indication of where Republicans feel the race is right now.

Also note that the GOP-aligned Jobs Coalition tweaked Walz for his one-time backing by the National Rifle Association. That could drive a wedge between progressive urban voters who hate the gun lobby and Walz, as he tries to broaden his base beyond his southern Minnesota congressional district.

A GOP source who knows southern Minnesota has much respect — actually, maybe fear is the word — for Walz’s political skills, comparing him to the late Sen. Paul Wellstone. He’ll be the nominee and Republicans better be ready, says this person.

On the other side, a DFL source says Walz, while occasionally suffering from “loquaciousness,” has otherwise impressed potential delegates around the state in his travels thus far.

Back on the Republican side, Minnesota House Speaker Kurt Daudt, R-Crown, is still assessing the race, his camp told me last week. The speaker, who bolstered his case in the past year by unexpectedly expanding his House majority and getting a package of tax cuts and road spending through the legislative session in May, has said he will announce a decision in late summer or early fall.

Another name that continues to pop up, a GOP operative told me last week: former Gov. Tim Pawlenty. If Daudt does not get in, suddenly the Republican field looks a bit underwhelming, and the Pawlenty speculation will ramp up.

The State Fair will be a big opportunity for members of the crowded field on both sides to show their retail politicking skills. Remember candidates: Don’t get photographed wearing a funny hat or with a mouthful of food.