It's not Kasich, per
the Columbus Dispatch. Might be AG Mike DeWine, former Senator and U.S. Rep from Ohio, which would make sense. Ohio Senate President Ton Niehaus' camp also denied comment to reporters, but given Santorum's positions and the bills Niehaus has been helping push through the state Senate recently, I wouldn't be surprised if it was BOTH of them. DeWine on his own is not really a big enough announcement for this.
EDIT: Oh, guess it is DeWine. Fun fact: his second cousin runs the Ohio GOP.