Maricopa County Sheriff Joe Arpaio led a field of potential Republican Senate candidates in Arizona with 21 percent in a poll of likely GOP primary voters last week.

Rep. Jeff Flake, who announced his candidacy for the seat of retiring Senate Minority Whip Jon Kyl (R-Ariz.) on Monday, finished second with 16.8 percent in the Summit Consulting Group survey. Former Rep. J.D. Hayworth took third, with 16.6 percent. He was unsuccessful in his primary challenge to Sen. John McCain last year.

The auto-dial poll of 1,881 likely GOP primary voters was conducted Thursday. It had a margin of error of 3 percentage points, which would put the top three finishers in a statistical tie.

Coming in fourth was former Rep. John Shadegg at 12 percent, followed by freshman Rep. Ben Quayle at 6 percent. A significant percentage of respondents, 27.5 percent, were undecided.

Arpaio has made national headlines over the years for his tough stance on crime and illegal immigration. It was unclear how much interest he has in running for Senate versus running for re-election as sheriff, but he is being urged by his supporters to pursue the Congressional seat, according to a GOP strategist in Arizona.