Topeka (AP) — A Washington-area group is spending more than $423,000 on radio and television ads in Kansas markets to boost tea party challenger Milton Wolf’s campaign against U.S. Sen. Pat Roberts in the Republican primary, and the group’s leader said Monday that the effort signals the race is tightening.

But a top Roberts campaign aide said the Senate Conservatives Fund in Alexandria, Va., is trying vainly to “rescue” Wolf ahead of the Aug. 5 election because Wolf is a flawed candidate. Wolf is a Leawood radiologist making his first run for public office, while Roberts is seeking his fourth, six-year term in the Senate.

A 30-second TV spot and a 60-second radio spot from the fund’s super PAC began last week and join a flurry of ads from the Roberts and Wolf campaigns that also started last week.

The newest Roberts ad criticizes Wolf for failing to vote in local elections and state primaries 28 times since 1997. Separately, Wolf’s latest ad and the Senate Conservative Fund PAC spots attack Roberts as out of touch because of his long tenure in Washington.

The fund’s PAC, Senate Conservatives Action, disclosed its spending in a report filed with federal regulators last week. Ken Cuccinelli, the Senate Conservative Fund’s president, said Wolf remains the underdog but the group wouldn’t be jumping in if Roberts were not vulnerable.

“You can just consider us all sharks in the water, because we smell blood,” said Cuccinelli, a former Virginia attorney general who ran for governor in that state last year. “The grassroots support Dr. Wolf has been getting smells it, too.”

Roberts executive campaign manager Leroy Towns said the Senate Conservatives Fund will “talk a big line” but isn’t broadcasting ads as frequently as the senator’s campaign. He said Roberts was spending $140,000 a week on its spots.

Towns also said Cuccinelli’s group is making a “token” effort to boost its own fundraising. He said the suggestion in the anti-Roberts ad that he’s a liberal is “scurrilous.”

“It’s a very, very big hill to climb because Kansans know better,” Towns said.

Meanwhile, Wolf plans to spend about $350,000 and $400,000 total on his ads, spokesman Ben Hartman said.

Wolf’s latest ad and the Senate Conservatives Fund spots highlight a Roberts gaffe during an early July interview on a Kansas City-area radio station. Wolf has repeatedly attacked Roberts because his official residence in Dodge City is rented space in the home of two supporters.

Roberts said, “Every time I get an opponent — uh, I mean, every time I get a chance — I’m home.”

But the senator’s ad starts with an issue vexing Wolf. 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.

The Roberts spot ties the issue to Wolf’s repeatedly not voting in elections and labels him, “unethical” and “irresponsible.” Hartman called the criticism “bizarre,” but Towns said Wolf didn’t care about issues, such as taxes and water, that were important to his neighbors.