PHOENIX – In terms of “major” as United States Senate candidate J. D. Hayworth billed his announcement here outside the McCain 2010 headquarters, let’s give it a feh. But as political theater goes, it wasn’t bad. Mr. Hayworth, whose challenge to Mr. McCain is now one of the more closely watched primary contests in the country, strolled into the senior senator’s campaign office Thursday morning and handed the receptionist a letter requesting that Mr. McCain join him for debates or town hall meetings across the state between now and the August contest, a press gaggle on his heels.