The speculation has run rampant at times: Who will Mitt Romney pick as a running mate for November's election? One popular candidate is making the short list, it appears.

FOX News Radio's Jane Metzler reports in this election update:

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From America's Election Headquarters...

(Sen. Rubio) "I think everybody should just take a deep breath.  Governor Romney's gonna make a great choice."

Florida Sen. Marco Rubio, on reports he's not even being considered as a possible running mate by the presumptive Republican nominee, which Romney himself disputes.

(Romney) "The story was entirely false.  Marco Rubio is being thoroughly vetted as part of our process."

The reports about Rubio, quoting unnamed advisers.  Romney says he and a longtime aide are the only ones who know who's being considered, and they're keeping the process quiet.

Jane Metzler, FOX News Radio.

WATCH more on Romney vetting Rubio HERE: