Marco RubioMarco Antonio RubioHillicon Valley: Biden administration sanctions Russia for SolarWinds hack, election interference Senators reintroduce bill to block NATO withdrawal New US sanctions further chill Biden-Putin relations MORE regrets his personal attacks against his GOP competitor for the White House Donald TrumpDonald TrumpBiden administration still seizing land near border despite plans to stop building wall: report Illinois House passes bill that would mandate Asian-American history lessons in schools Overnight Defense: Administration says 'low to moderate confidence' Russia behind Afghanistan troop bounties | 'Low to medium risk' of Russia invading Ukraine in next few weeks | Intelligence leaders face sharp questions during House worldwide threats he 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 CruzCruz no longer wearing mask in Capitol The Hill's Morning Report - Presented by Tax March - CDC in limbo on J&J vax verdict; Rep. Brady retiring Democrats brace for new 'defund the police' attacks 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."