A.J. Baime poses a provocative idea as the basis of his book on Harry Truman: No American president faced a tougher four months in office that Truman had in the spring and summer of 1945.

“It’s a very inspirational story,” he says.

Baime spoke Thursday night in Kansas City, and it was recorded for C-SPAN. His new book is “The Accidental President: Harry Truman and the Four Months that Changed the World.”

Truman was still relatively unknown when he became president on April 12, 1945, at the death of Franklin D. Roosevelt. Just the fall before, only 55 percent of the American people, in a poll, could identity FDR’s running mate.

Now he was president. Many wondered and some doubted if he was up to the job. The difference, Baime said, is that he drew on his strength of character and vowed to do his best.

“And he rolls up his sleeves and he gets to work,” Baime said.

A lot landed on Truman’s plate right away: the fall of Berlin and the end of World War II in Europe, the Potsdam Conference that shaped post-war Europe, the conference to found the United Nations, the beginnings of the Cold War – and the decision to use the atomic bomb to end the war in the Pacific.

“Still today this decision is the most controversial that any president has ever made,” Baime said.

Which of those crises and decisions was a biggest in that four-month period?

“It’s hard to say one was more important than the other,” Baime said, “because they stack up on one another.”

Truman got to work, and people around him, then others in Washington, then the country began to see that there was a good deal more to him that they thought. He knew history and government, he gathered information and made decisions, and he talked straight.

“People asked him a question, and he answered it,” Baime said.

This showed results. Two months into his presidency, one poll said 63 percent of Americans thought he should be the Democrats’ nominee in 1948. (He was, and he won.) Three months in, Gallup put his approval rating at 87 percent.

“That’s extraordinary,” Baime said. “Can you imagine that number today?”

Baime focused at some length on Hiroshima and Nagasaki. At Hiroshima alone, the U.S. government has estimated, 200,000 people died in the Aug. 6, 1945, atomic bombing.

What were the motivations of Truman and other American leaders? Sending a message to the Soviet Union? Racism toward the Japanese?

“We can never know 100 percent what was going through the president’s mind,” Baime said.

He leans toward the most straightforward explanation.

Earlier in 1945, America had fought and won two of the bloodiest battles in its history.

“We know that they (Japan) refused to surrender at Iwo Jima and Okinawa,” Baime said.

Neither did 100,000 deaths during the firebombing of Tokyo seem to lessen Japan’s resolve to fight on.

Truman, sticking with the demand for unconditional surrender that the Allies had demanded throughout the war, was looking at Nov. 1, 1945, and the planned invasion of Japan with 766,700 American troops.

“We knew from Okinawa and Iwo Jima it was going to be very bloody,” Baime said.

Truman chose to incinerate two Japanese cities – it did abruptly end the war, with unconditional surrender – instead of sacrificing so many young Americans.

“As for whether it saved lives, we cannot know,” Baime said.

He said it was, as Secretary of War Henry Stimson wrote later, “our least abhorrent choice.”

“Leaders – strong leaders – they make decisions,” Baime said, “and they live with them the rest of their lives.”