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In fact, during a town hall event in Colorado earlier this week, a supporter asked Romney if he'd be making his choice "before or after" the convention.

"Yes," Romney quipped, drawing laughs from the crowd.

But Romney provided little insight beyond that, telling supporters at the Colorado event he couldn't provide more of a timeline on his vice presidential selection.

Instead, the Republican hopeful simply pledged that "the person I choose you will look at and say 'that person could be president if necessary.'" But who that person could be remains the subject of intense speculation.

Among the possibilities: Sen. Marco RubioMarco RubioMcConnell on Trump: 'We could do with a little less drama' Taking the easy layup: Why brain cancer patients depend on it Rubio: 'All options should be on table' if Flynn refuses new subpoenas MORE (R-Fla.), who Romney himself confirmed was under consideration, and Sen. Rob PortmanRob PortmanGOP senators bristle at Trump's Medicaid cuts Overnight Energy: Trump budget takes flak over oil provisions GOP senators knock Trump's budget proposal MORE (R-Ohio), who told ABC News earlier this week that he had met multiple times with Romney's vetting team.