Manning's teaching career was interrupted by the U.S.-Mexican War, and he left for Texas in June, 1916 as commander of the Charleston Light Dragoon, a National Guard unit.
During his tenure in the State House, Manning served on the powerful Ways and Means Committee and sponsored a variety of bills.
In the 1934 gubernatorial election, Manning placed third in the Democratic primary, losing to Olin D. Johnston and Coleman Livingston Blease.
This time, he fared better, defeating Blease and placing second to Burnet Rhett Maybank with a strong enough result to qualify for the runoff, which he lost by less than 15,000 votes.
Again, Manning again returned to farming, but decided to run a third time in 1942 election, facing off against his old opponent, Olin Johnston.