We use the three lepton and missing energy trilepton signature to search for chargino-neutralino production with 2.0 fb;{-1} of integrated luminosity collected by the CDF II experiment at the Tevatron pp[over ] collider. We expect an excess of approximately 11 supersymmetric events for a choice of parameters of the mSUGRA model, but our observation of 7 events is consistent with the standard model expectation of 6.4 events. We constrain the mSUGRA model of supersymmetry and rule out chargino masses up to 145 GeV/c;{2} for a specific choice of parameters.