 Complete the following phrase:  Johnston was enthusiastic about the outbreak of the MexicanAmerican War. He served on the staff of Lt. Gen. Winfield Scott in the Siege of Veracruz, having been chosen by Scott to be the officer carrying the demand for surrender beforehand to the provincial governor. He was in the vanguard of the movement inland under Brig. Gen. David E. Twiggs and was severely wounded by grapeshot performing reconnaissance prior to the 