Ted Cruz will grab an upset win over Donald Trump in Arizona's presidential primary election on Tuesday, as he's the "only candidate with any kind of organization out here," a close confidant of Sen. John McCain predicts."They have him positioned to spring the upset," Kurt Davis , a GOP operative in Arizona, told The Hill. "They just have to deliver."The winner of Tuesday's Arizona primary in the largest winner-take-all state will scoop up all 58 of its delegates, marking a key win as the GOP convention in Cleveland nears. If Trump takes the delegates he'd move closer to securing the nomination, but a loss to Cruz could make a contested convention even more likely.According to Real Clear Politics , Trump is ahead of Cruz by 13 points in the state's polls, but in Arizona, Republicans on the ground say the race's margin is narrower, and Cruz could pull off the upset.There have been no polls done since Marco Rubio backed out of the contest, The Hill reports, and earlier polling samples have been small. Further, many voters are expected to decide at the last minute.Trump and Cruz are both making a late push in Arizona over the weekend, while Ohio Gov. John Kasich is concentrating on Utah. Trump was returning to Arizona Saturday, after speaking in Salt Lake City Friday night.Cruz, meanwhile, held a press conference at Arizona's southern border Friday and held a rally with former Texas Gov. Rick Perry, former GOP contender Carly Fiorina, and Glenn Beck later in the day.Arizona holds a closed primary, allowing only Republicans to vote, which may also play in Cruz's favor. But Trump is being backed by Maricopa County Sheriff Joe Arpaio and former Gov. Jan Brewer, two powerful figures in the state.