President Obama on Thursday slammed Sen. Marco RubioMarco Antonio RubioOn The Money: Dems set Tuesday vote on Trump's emergency declaration | Most Republicans expected to back Trump | Senate plots to avoid fall shutdown drama | Powell heading before Congress Brown, Rubio trade barbs over ‘dignity of work’ as Brown mulls presidential bid The Hill's Morning Report — Emergency declaration to test GOP loyalty to Trump MORE (R-Fla.) and other GOP lawmakers for continuing to support Republican presidential nominee Donald TrumpDonald John TrumpAverage tax refunds down double-digits, IRS data shows White House warns Maduro as Venezuela orders partial closure of border with Colombia Trump administration directs 1,000 more troops to Mexican border MORE.

Obama noted that Rubio called Trump a "con artist" while the two were battling it out in the GOP primaries.

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"Now that begs the question, since we're in Florida, why does Mr. Rubio still plan to vote for Donald Trump?" Obama said during a rally for Democratic presidential nominee Hilary Clinton in Miami.

Obama, who was also campaigning on behalf of Rubio's Democratic Senate challenger, Rep. Patrick Murphy, said, "There has to be a point where you stand for something more than just party, or more than just your own career."

"How can you call him a con artist and dangerous and object to all the controversial things he says and then say, 'But I'm still going to vote for him.' Come on, man. Come on, man," Obama said.

"That's a sign of somebody who will say anything, do anything, pretend to be anybody, just to get elected," Obama said.

Rubio is locked in a tight race with Murphy as Republicans look to maintain their Senate majority after the election. Rubio has a 5-point lead over Murphy, 47-42 percent, according to the RealClearPolitics polling index.