He'd probably be narrowly leading Bachmann and Huntsman, be even with Perry, trail Giuliani by a point or two, and trail Romney by 5-6 points.
Legitimate battleground against Romney, and he probably beats everyone else who is an imaginable nominee. He was leading
Huckabee in April, so he would probably crush Perry and Bachmann, both of whom have shown themselves to have deep problems with credibility.
President Obama will campaign in Arizona on behalf of the Democrat who runs for the open Senate seat, and I expect the Democrats to have a strong GOTV drive in Arizona irrespective of who the Republican nominee is..