This joke comes from the laugh-fest that was the Civil War. See, the Union commander-in-chief was General George McClellan. He was horrible! McClellan was so indecisive, he refused to go into battle unless he KNEW he would win.
Abe went to visit George McClellan at his new headquarters. Attracted to the sounds of hammering, Abe found a soldier building an outhouse near the general’s quarters.
“Will that be a one-holer or a two-holer?” Abe asked. (Outhouses that could seat two people were called “two-holers.”
“A one-holer, Mr. President,” the soldier answered.
“Thank goodness,” Abe said. “If it was a two-holer, George would poop his pants before he could make up his mind which one to use.”