Attack ads from both fellow Republicans and supporters of Senator Kay Hagan are lowering support for North Carolina Speaker of the House Thom Tillis, in his bid for Hagan’s U.S. Senate seat.

That’s according to Public Policy Polling numbers released Monday.

Tom Jensen, the director of the Raleigh-based polling firm, says that while Tillis remains the front runner in a primary race against Greg Brannon and Mark Harris, he’s been weakened to a degree that increases the chance of a runoff.

But only slightly.

“We still find Thom Tillis at the 40 percent mark that he needs to avoid a runoff,” says Jensen. “But he’s lost some ground compared to a week ago, when he was at 46 percent. Greg Brannon and Mark Harris do have the momentum in the closing stage of the race.”

At 28 percent, Brannon is up eight points from a week ago. And Mark Harris is at 15 percent, which is up four points from a week ago.

Still, 11 percent of voters are undecided, so Jensen still rates Tillis as the likely Republican primary winner.

Senate Majority PAC, which supports Hagan, has already spent nearly $1 million on TV ads that highlight scandals involving his former chief of staff Charles Thomas, who resigned after his affair with a home builders association lobbyist was revealed; and Tillis’s former policy adviser Amy Hobbs, who also had an affair with a lobbyist, and later resigned.

The ad also slams Tillis for giving those two former staffers a combined total of $19,333 in severance pay.

“Democratic groups have been trying to weaken Tillis by exploiting the staffer scandals,” says Jensen, “and also by bringing attention to his semi-positive comments he made about Obamacare a couple of months ago.”

During an interview with Bill LuMaye on WPTF in February, Tillis called the Affordable Care Act “a great idea that can’t be paid for.” In a recent Hagan ad, the quote is edited down to the “great idea” part.