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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 Antonio RubioColbert: Students taking action on gun violence 'give me hope' Lawmakers feel pressure on guns Florida lawmaker's aide fired after claiming shooting survivors were 'actors' MORE (R-Fla.), who Romney himself confirmed was under consideration, and Sen. Rob PortmanRobert (Rob) Jones PortmanCommittee chairman aims for House vote on opioid bills by Memorial Day Flake to try to force vote on DACA stopgap plan Congress punts fight over Dreamers to March MORE (R-Ohio), who told ABC News earlier this week that he had met multiple times with Romney's vetting team.