Irvin McDowell's beaten and demoralized army staggered back into Washington after the stunning Confederate victory at the First Battle of Bull Run, the realization came that the war might be prolonged, and efforts began to fortify the city in case of a Confederate assault.Lincoln knew he had to have a professional and trained army to protect the Capital area, and therefore began by organizing the Department on the Potomac on August 4, 1861, and the Army of the Potomac 16 days later.