Conservative Nebraska Senate candidate Ben Sasse has opened up a 14-point lead in the latest poll before Tuesday’s GOP primary.

A Magellan Strategies survey of likely GOP primary voters, 92% of whom said they would definitely vote in the May 13 primary, found Sasse leading with 38%, while liberal Republican Sid Dinsdale is in second with 24%. Establishment Republican Shane Osborn, who is backed by Senate Minority Leader Mitch McConnell (R-KY), is in third with 20%.

Sasse is endorsed by former Alaska Gov. Sarah Palin, Sens. Ted Cruz (R-TX) and Mike Lee (R-UT), conservative talk radio host Mark Levin, the Club for Growth, the Senate Conservatives Fund, Rep. Paul Ryan (R-WI), the Madison Project, and Citizens United, among others.

Sasse’s campaign started to gain momentum when he staunchly opposed Obamacare and blasted the Washington establishment for not fighting fiercely enough to defund it. That angered McConnell, who has backed Osborn, and groups that have falsely attacked Sasse on the Obamacare issue. Citizens United, though, ran a commercial for Sasse that featured Lee, the architect of the defund-Obamacare strategy, vouching for Sasse’s conservatism and opposition to Obamacare.

“Don’t be fooled by false attacks against conservative Ben Sasse,” Lee says in the ad. “Ben Sasse has always opposed Obamacare. Period.”

Dinsdale has recently been assailed as a “counterfeit conservative” for having donated to liberal Democrats. His family members have had prominent positions with Planned Parenthood, and Dinsdale has said that he would always vote to raise the debt. He has also taken the position that pro-life issues are not worth fighting for right now.

Sasse has surged, as evidenced by his 14-point lead, after Nebraskans became aware of Dinsdale’s liberalism and Osborn’s ties to McConnell. Last week, Sasse led by six points.

Sasse also has the highest favorability rating at 59% in the survey, which was conducted on May 8 and has a margin of error of +/- 4.28 percentage points.