Check your math. He finished FDR's 4 years (minus a month or so), then did 4 more years after Dewey defeated him in 1948.
Looks like 8 years before he went back to the haberdashery.
You are correct. I was counting the 4 years he was elected as President. The first almost 4 were “inherited”. I do remember.. I voted for the first time after Truman went back home.
I also remember when the war in Europe was over.. the celebrations.. the ones who paid the ultimate price.. the landing on Normandy with the Germans on the hill shooting our men as they tried to get enough ashore .. my father said they were to take the weapons and supplies of the dead as they ran past them.. if they could .. and to keep running to get ashore. It was a horrible war. It lasted too long. And Truman did what he thought was right. Not sure Roosevelt would have.