Marco RubioMarco Antonio RubioRubio in Colombia to push for delivery of humanitarian aid to Venezuela On unilateral executive action, Mitch McConnell was right — in 2014 On The Money: Trump declares emergency at border | Braces for legal fight | Move divides GOP | Trump signs border deal to avoid shutdown | Winners, losers from spending fight | US, China trade talks to resume next week MORE regrets his personal attacks against his GOP competitor for the White House Donald TrumpDonald John TrumpRosenstein expected to leave DOJ next month: reports Allies wary of Shanahan's assurances with looming presence of Trump States file lawsuit seeking to block Trump's national emergency declaration MORE, he told MSNBC Wednesday. 

"In terms of things that have to do with personal stuff, yeah, at the end of the day it's not something I'm entirely proud of," Rubio told the network in a town hall on Wednesday night. 
 
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"My kids were embarrassed by it, and if I had to do it again I wouldn't." 

Rubio had previously shied away from direct confrontation with Trump, but he burst out of the gate in the last debate before Super Tuesday by emptying the opposition research file against Trump.
 
The next morning, he bashed the billionaire as a "con artist" on television and days later poked fun at Trump's hands for being small.

"You know what they say about men with small hands?" Rubio said at a Feb. 26 rally. "You can’t trust them.” 

Despite the more aggressive tack, the Florida senator hasn't gained traction in the GOP nomination fight, falling hundreds of delegates behind Trump and Ted CruzRafael (Ted) Edward CruzEl Chapo's lawyer fires back at Cruz: 'Ludicrous' to suggest drug lord will pay for wall Democrats have a chance of beating Trump with Julian Castro on the 2020 ticket Poll shows competitive matchup if O’Rourke ran for Senate again MORE. His campaign has pinned all of its hopes on next week's Florida primary. 
 
At the same time,he told host Chuck Todd, "he needed to be stood up to."
 
Rubio also told MSNBC that he wouldn't be anyone's running mate -- including Trump's -- if asked. "I'm running for president."