A Washington-area group backing tea party challenger Milton Wolf’s bid to unseat Kansas Sen. Pat Roberts is spending more than $423,000 on radio and television ads ahead of the Republican primary.

The ads from a political action committee tied to the Senate Conservatives Fund also are mixing with the candidates’ own statewide spots.

Senate Conservatives Fund President Ken Cuccinelli said Monday that Wolf remains the underdog against three-term incumbent Roberts but the fund believes Wolf can win.

Wolf is broadcasting his own television ad, noting that the senator’s official residence in Dodge City is rented space in a home owned by supporters. The conservative group’s ad hits similar themes.

Roberts’ campaign began a television ad last week blasting Wolf for repeatedly not voting in local elections and state primaries.