Kansas Sen. Pat Roberts stoked the political brushfire he was hoping to smother during a recent Kansas City-area radio morning show.

"Every time I get an opponent — uh, I mean, every time I get a chance — I'm home," Roberts said during the KCMO interview.

That's just Milton Wolf's point. The tea party-backed challenger for the GOP nomination has been casting the third-term senator as a Washington politician who has lost touch with his constituents. The charge is a potent one already in the 2014 midterm elections: It was a key factor in the ouster last month of House Majority Leader Eric Cantor of Virginia. The accusation nearly cost veteran Mississippi Sen. Thad Cochran the GOP nomination, and remains a challenge for him.

Wolf rests much of his case on Roberts' living arrangements. The senator owns a Washington-area home while his official residence in Dodge City is rented space in a home owned by two supporters. Not so long ago, Roberts joked about having full access to a recliner there.

It's no laughing matter now. The "residency issue" has given some GOP voters pause, even if they believe Roberts has represented the state well during a 47-year career in politics.

"I wish he'd get his residency problem fixed instead of joking about it," said Henry Ratcliff, a 63-year-old retired Augusta aviation mechanic. "If it wasn't for that, I wouldn't consider voting for anybody else but Pat Roberts."

The 78-year old Roberts is widely expected to win the GOP nomination over Wolf, a 43-year-old radiologist and first-time candidate, in the Aug. 5 primary. The power of incumbency and the campaign war chest that goes with it are considerable advantages.

And Wolf has weaknesses Roberts has targeted. The challenger has acknowledged that several years ago he posted graphic X-ray images of fatal gunshot wounds and other medical injuries on a personal Facebook page, along with dark-humor commentary. Wolf apologized, but Roberts suggests in radio and television ads that "ethics" issues dog the challenger.

At a recent event in Augusta — a town east of Wichita — Roberts not-so-subtly suggested that Republicans don't need any surprises as they seek the six-seat gain they need to wrest control of the Senate from Democrats in November.

"Kansans know my record. They're part and parcel of the partnership we've had," he said. "Nobody knows Kansas better than I do, and we've built a good partnership. I do not think that would be the case with my opponent."

Retorted Wolf: "He still at this point is clinging to a name recognition advantage."

But the residency question has Roberts' attention.

Before speaking at the Augusta event, Roberts shed the dark suit jacket and baby-blue tie he'd worn at an earlier public event and rolled up the sleeves of his no-longer-crisp white shirt, and reminded the audience, as Cochran did in Mississippi, that Senate seniority can mean good things for a senator's home state.

Should the GOP win the Senate majority, Roberts stands a good chance of being the next chairman of the Agriculture Committee, giving him an opportunity to shape farm policy while representing the nation's leading wheat-producing state and one of its top beef providers.

But much of his pitch revolved around the value of a longtime senator who, unlike Wolf, is a "known product."

The son of a state GOP kingmaker and confidant of Dwight Eisenhower, Roberts began working as a congressional staffer in 1967, won the House seat for western and central Kansas in 1980 and captured his Senate seat in 1996. And he helped with enough big Kansas projects over the years that a biosecurity research institute at Kansas State University bears his name.

Roberts and Wolf face two lesser-known candidates in the GOP primary. Two Democrats also are running: Shawnee County District Attorney Chad Taylor and Lawrence attorney Patrick Wiesner.

But history favors the GOP in Kansas. Republicans have won every Senate race in the state since 1932. Beside a big advantage in campaign cash, Roberts has the backing of key conservative groups that are core constituencies for the state GOP, including Kansans for Life and the Kansas State Rifle Association.

Wolf dismisses questions about whether the general election race will be more volatile if he's the GOP nominee and rejects Roberts' arguments that the X-ray postings are a serious issue for voters.

While campaigning, Wolf highlights conservative positions on issues such as health care and gun rights that have brought him backing from tea party adherents and played up his status as a distant but critical relation of President Barack Obama. But his outsider's status and relative youth may represent his biggest appeal.

Caitlin Pretzer, a 21-year-old Salina resident and fast-food worker hoping to save money to study psychology, came to the Abilene town hall with a friend who supports Wolf and liked what she heard from the challenger. Roberts, she said, has "been there too long."

Roberts does own a duplex unit in Dodge City but actually rents it out — acknowledging during the radio interview, "That was probably a mistake."