SHORTLY before leaving office, Harry Truman invited the American people to contemplate the magnitude of the US Presidency: “There is no job like it on the face of the earth – in the power which is concentrated here at this desk, and in the responsibility and difficulty of the decisions.”

With the mind-boggling Mr Trump riding high in the polls, it might be prudent to have Truman’s words plastered on every available flat surface from sea to shining sea. If that’s not feasible, the citizenry should at least be encouraged to read William Leuchtenburg’s outstanding new book. Its 900 pages will make Americans think very hard about the kind of person they want in the Oval Office. This is “a chronicle of those not-so-faraway times when lions – often magnificent, sometimes feckless or perfidious – roamed the land.”

Truman roared louder than most, and not every resident of the 20th-century White House can comfortably be described as leonine. Calvin Coolidge, Leuchtenburg writes, “may well have been the least magnetic personality in the history of the executive office.” No amount of publicity stunts – inviting Al Jolson over for breakfast, and so forth – could do much to bolster his public image. Warren G Harding, meanwhile, will largely be remembered for his rambling orations, described by one contemporary as “an army of pompous phrases moving over the landscape in search of an idea”. Nor was being a decent chap sufficient to make a memorable president: Jimmy Carter “was, and is, a very good man... he was just not very good at his craft”.

Other presidents were able to wow the crowds, but popularity is not synonymous with greatness. “No other man in the 20th century entered the White House with so lustrous a reputation as Dwight David Eisenhower,” Leuchtenburg writes, and the fanfared “liberator of Europe” was also blessed with a “genial manner and infectious grin”. Through his term his average approval rating was 64 per cent – “an astonishing figure” – but history will also recall his lacklustre engagement with the cause of civil rights and his frequently haywire foreign policy. Ronald Reagan was another people’s favourite, and Leuchtenburg credits him with a rare ability for persuasion and moments of inspirational statesmanship. Leuchtenburg also reminds us, however, that “no-one had ever entered the White House so grossly ill-informed” .We thought we saw the “bighearted guy who liked nothing better than to mix with folks, but he was chillingly insular”.

When ranking presidents, we can feel a little sorry for those who had hard acts to follow. William Howard Taft’s predecessor, Theodore Roosevelt, was the president who, earlier in life, had climbed mountains, killed Spanish soldiers, and punched out drunks in bar-room brawls. Henry James called him the “embodiment of noise” but Teddy also had depth: he read Dante in Italian and could recite passages from the Chanson de Roland. Taft could not compete. He was obese, played “slow-paced rounds of golf,” and was compared to “an American bison – a gentle kind one”. Lyndon Johnson also had it tough. He was “colossally egocentric” – when the pope gifted him a Renaissance painting, LBJ gave a bust of himself to the bishop of Rome – but following the slain king of Camelot was a tall order. Kennedy was not a wonderful president but he cast the longest of cultural shadows.

For the true greats, of course, timing didn’t matter a jot. Truman had to follow the mighty Franklin Roosevelt. We could argue all day about the efficacy of FDR’s policies but no-one could sensibly question the man’s courage and determination. Truman was initially cowed by the legacy – in sticky moments he would phone FDR’s widow to ask what the great man might have done – but he soon came into his own. Truman’s plain-speaking was sometimes excessive and he made mistakes – allowing anti-Communist paranoia to fester at home and overreaching in Korea. The dropping of atomic bombs on Japan also brought tragedy but this was a strategic decision, for which Truman took full responsibility, not an act of moral wickedness. Any president would likely have taken the same course in the circumstances.

The roster of achievements is, meanwhile, impressive, from the Marshall Plan to incredibly brave, if often forgotten, engagement with the emerging civil rights movement. Leuchtenburg tells us that Truman had a “profound respect” for the office of president and, while never dismissing sage counsel, he trusted his beliefs and instincts.

“I wonder how far Moses would have gone if he had taken a poll in Egypt,” he once wrote. Regrettably, it is hard to see what “the Donald” has in common with Harry Truman beyond the first four letters of their surnames.