Newark mayor Cory Booker sent out a series of impassioned tweets Thursday evening in response to continuing fallout from his appearance on "Meet The Press" last Sunday, in which he expressed discomfort with the Obama campaign's strategy of attacking Mitt Romney over his career in private equity. "Sorry I make u sick," one tweet read. "And sorry I made a mistake. I'm sorry that 15 seconds on MTP erodes my 20 yrs of work in inner cities around our nation."

A second tweet struck a more reflective tone:

Finally, Booker addressed the chasm between his opinions and the presidential campaign for which he is seen as a surrogate:

Booker told "Meet the Press" host David Gregory that he found President Obama's ads attacking Bain Capital, Romney's former company, "nauseating." Hours after the appearance, Booker backtracked, but Republicans quickly made him a campaign talking point. Many Democrats and left-leaning commentators also expressed outrage with Booker for breaking with the president.

Below, Obama surrogates to keep an eye on this election cycle.

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  • Chicago Mayor Rahm Emanuel

  • Massachusetts Gov. Deval Patrick

  • Montana Gov. Brian Schweitzer

  • Former Pennsylvania Gov. Ed Rendell

  • Newark Mayor Cory Booker

  • N.Y. Gov. Andrew Cuomo

  • Sen. Jon Tester (D-Mont.)

  • L.A. Mayor Antonio Villaraigosa

  • Sen. Jim Webb (D-Va.)

  • Former President Bill Clinton

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