A popular political website that attempts to predict the outcomes congressional races has flagged Arizona’s U.S. Senate race as one to watch.

Sabato’s Crystal Ball, a free non-partisan online newsletter, wrote this week about Republican-held Senate seats that could be in play across the country. The article highlights the race in Arizona to replace longtime U.S. Sen. Jon Kyl, a Republican who is retiring after 18 years.

“Another seat that bears watching is in Republican-leaning Arizona, where Democrats love their candidate — former Bush administration Surgeon General Richard Carmona — and the GOP has an unexpectedly hot primary brewing between Rep. Jeff Flake and outsider, self-funding businessman Wil Cardon," the article says.

“Flake recently called in the big guns, getting endorsements from Arizona Republican Sens. John McCain and Jon Kyl (whose retirement has opened up this seat). Flake also has the support of the Club for Growth, which is generally known for backing insurgents, but not in this instance. Yet Arizona Republicans might not think that Flake is sufficiently hard-line on immigration, and Cardon has boatloads of money to spend.

“Against Flake, Carmona’s a competitive underdog; against Cardon, it could very well be a toss-up race.”

Carmona, who is running unopposed in the Democratic primary for U.S. Senate on Aug. 28, posted this on his Facebook page today in response to the article: " I'll take that, I've been an underdog all my life."

Flake and Cardon are joined on the GOP ballot by former Youngtown mayor Bryan Hackbarth and radio talk show host Clair Van Steenwyk, better known as ‘Van the Radio Man.’

The winner of the Flake-Cardon matchup will enter the general election with a built-in advantage because there are nearly 183,000 more registered Republican voters than Democrats in Arizona. There are 94,500 more independent voters than Democrats, too.

Stay tuned to the Pueblo Politics blog throughout 2012 for news, updates and information about Arizona politics. You can follow Arizona Daily Star reporter Brady McCombs on Twitter by clicking on his name.