Dr. Kelli Ward may end up pulling off a surprise victory against longtime incumbent Sen. John McCain (R-AZ) on Tuesday, as new polling from Breitbart News Network and Gravis Marketing shows a razor thin lead for McCain.

Ward, a former state senator who stepped down from that post to focus on the U.S. Senate race, trails McCain with Arizona Republicans by just four points heading into election day. Ward gets 33 percent in the latest Breitbart/Gravis poll compared to McCain’s 37 percent. Twenty-three percent of the likely GOP primary voters are undecided walking into election day.

Arizona Senate Primary Poll for Public Release by Breitbart News on Scribd

The Senate GOP primary poll was conducted on August 27, and included 780 likely GOP primary voters. This particular part of the survey on just likely GOP Senate primary voters—other parts focused on the general election and various issues and sentiment in the state—has a margin of error of 3.4 percent. The other parts of the survey will be released soon.

“McCain can feel good about his four-point lead, but he should also feel anxious about the 23 percent of the Republican voters telling us they are unsure,” said Doug Kaplan, the managing partner of Gravis Marketing the Florida-based firm that executed the poll.

“The other thing that should make McCain worry is that Ward is holding him below 50 percent, which is a critical benchmark for an incumbent,” Kaplan said.

Longtime Democratic pollster Patrick Caddell, who worked for President Jimmy Carter, told Breitbart News the poll proves that the Arizona GOP Senate primary is a close race and it will be determined by who shows up on primary day. Arizona’s early voting will also play an interesting role, he said.

“We see that the early voters favor McCain and the later voters favor Ward,” he said.

“Another twist that goes against McCain is that the less likely voters are backing him and the more likely voters are backing Ward,” Caddell added.

Arizona has early voting for the primary which started at the beginning of the month, and of those 780 likely GOP primary voters—which includes independents since in Arizona independents are allowed to vote in primaries—39 percent said they voted early while 61 percent said they didn’t. McCain led by a sizable margin among those who voted early, with 46 percent saying they pulled the lever for the senior Arizona senator, 35 percent for Ward and 19 percent for someone else.

Either McCain or Ward would smoke likely Democratic U.S. Senate nominee and current Rep. Ann Kirkpatrick (D-AZ) in a general election matchup, too, the polling shows. Specifically, with McCain against Kirkpatrick, McCain wins 63 percent to Kirkpatrick’s 20 percent with 17 percent unsure. Ward, meanwhile, would beat Kirkpatrick 53 percent to 19 percent with 29 percent unsure.

The general election poll has a sample of 1,244 likely voters, with a margin of error of 2.8 percent.

Likely voters generally dislike McCain, too, as more than half—52 percent in total—view him as either “strongly unfavorable” or “somewhat unfavorable.” Only 42 percent view McCain as either somewhat or strongly favorable, while just 7 percent don’t know. Forty-two percent of voters viewed Ward as either strongly or somewhat unfavorable, while 38 percent thought she is strongly or somewhat favorable and 20 percent were unsure. Thirty-nine percent of likely voters surveyed viewed Kirkpatrick as either strongly or somewhat unfavorable, while 36 percent viewed her as either strongly or somewhat favorable and 25 percent didn’t know.

More questions on the poll will be released soon.