Miller and Treadwell ripped the front-runner for the Republican nomination for the short time he's spent in Alaska.
Treadwell hit Sullivan for his out-of-state fundraising, citing big donations from the employees of a company his brother in Ohio owns.
Sullivan responded by saying he'd had a similar trajectory as former Sen. Ted Stevens (R-Alaska) — he grew up in the Midwest and served in the military before moving to the state.
He has emerged as the front-runner in most polls and has a huge fundraising lead, partly due to his national connections. He worked in the Bush administration, and both he and his brother are close to Sen. Rob Portman (R-Ohio).
Treadwell has deeper ties in the state but has proven to be a weak fundraiser. The big question is whether attacks on Sullivan's tenure in the state damage his standing for the general election — Democrats have been pounding him on the issue as well.
The three are vying to take on Sen. Mark BegichMark BegichRyan's victory trumps justice reform opponents There is great responsibility being in the minority Senate GOP deeply concerned over Trump effect MORE (D-Alaska), who's running a top-notch campaign in the conservative state.
Sullivan also got some help on the air on Thursday, with American Crossroads, which has endorsed him, launching an ad saying Begich "takes credit" for things he didn't do and tying him to President Obama.