  We use the three lepton and missing energy "trilepton" signature to search
for chargino-neutralino production with 2.0 inverse femtobarns of integrated
luminosity collected by the CDF II experiment at the Tevatron ppbar 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.
