A real estate mogul and former Flake supporter, Cardon started out with little name recognition, but has been blanketing the airwaves with television ads introducing himself to Arizona voters and attacking Flake on energy and immigration. Cardon has already pumped more than $4 million of his own money into the race, leading Flake to argue that Cardon is essentially trying to buy the Senate seat.

Just 17 percent of Arizona voters knew who Cardon was in February, but in May, 35 percent recognized him. Flake, who has been in Congress for more than a decade, is recognized by six in ten voters.

Carmona is still an unknown to two out of three voters, giving him room to grow as more voters become acquainted with him in the general election. Carmona is the sole Democrat in the primary; another Democrat, Don Bivens, dropped out in March.

The poll of 500 Arizona voters was conducted May 17-20 using automated telephone interviews, and had an overall margin of error of plus or minus 4.4 percentage points.

The Hill rates this race as leaning Republican.