He kind of slipped up yesterday during a Skype interview:
"When I go out and campaign next year... for myself as a gubernatorial candidate or for another gubernatorial candidate should I decide not to run -- when I talk to crowds or to individuals advocating for whoever that candidate is, I'm not gonna do it on anything but the issues."
Elipses mine, because there's a very distinct pause after "next year" where he appears to have caught himself blabbing his plans. But only Booker knows for sure. I can tell you this: it'll be the toughest campaign of his career against a very popular Chris Christie. That said, Christie is terrible on policy and Booker could out-hustle him on that front.