Marco RubioMarco RubioDem senator: House Intel chairman may have revealed classified info Five takeaways from Labor pick’s confirmation hearing GOP insists FBI probe won’t slow up Trump MORE regrets his personal attacks against his GOP competitor for the White House Donald TrumpDonald TrumpOvernight Cybersecurity: House Intel chair says surveillance collected on Trump transition team Budowsky: Trump’s war against truth GOP chairman calls for tighter sanctions on Russia 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 CruzTed CruzBudowsky: Trump’s war against truth Five takeaways from Labor pick’s confirmation hearing Republicans should seize the moment and repeal ObamaCare now 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."