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President Donald Trump's argument that the removal of Confederate statues is a slippery slope to changing history has recharged the perennial debate about America's tormented racial legacy.

"So this week it's Robert E Lee," he said on Tuesday of the rebel general's monument that was a flashpoint for last Saturday's violent rally in Virginia.

"I wonder, is it George Washington next week?" he asked journalists at Trump Tower. "And is it Thomas Jefferson the week after?"

Let's put aside for a moment the irony that Lee may well have supported Charlottesville's plans to remove his bronze likeness, given that he urged the country to "obliterate the marks of civil strife" and refrain from erecting such monuments.

As President Trump pointed out, George Washington was a slaveholder.

So might the stone obelisk dedicated to the father of the nation, looming over the heart of his eponymous capital city, be the next battleground in the US culture wars?

Or even Mount Rushmore?

Washington conceded the system of human bondage that underpinned the economy of 18th Century Virginia was a "wicked, cruel and unnatural trade".

He was the only founding father and commander-in-chief to liberate his slaves - he owned more than 300 - when he died.

But as Ron Chernow's magisterial biography Washington: A Life makes clear, while he lived, the nation's first president extracted his pound of flesh from those whom he preferred to call his "servants", or "family".

Washington saw himself as a benevolent master, but he did not tolerate suspected shirkers on his farm, even when they were pregnant, elderly or crippled.

Image copyright Getty Images Image caption This 1851 painting portrays Washington as a simple farmer

He once scolded a slave who pleaded that he could not work because his arm was in a sling.

As Chernow writes, Washington picked up a rake and demonstrated how to use it with one arm.

"If you use your hand to eat," he said, "why can't you use it to work?"

He was not averse to shipping refractory slaves to the West Indies, such as one man named Waggoner Jack, where the tropical climate and relentless toil in sugarcane brakes tended to abbreviate life expectancy.

"There are few Negroes who will work unless there be a constant eye on them," Washington advised one overseer, warning of their "idleness and deceit" unless treated firmly.

Washington, Chernow notes, wholly approved in 1793 when one of his estate managers, Anthony Whitting, whipped a slave named Charlotte.

Martha, the president's wife, had deemed her to be "indolent".

"Your treatment of Charlotte was very proper," Washington wrote, "and if she or any other of the servants will not do their duty by fair means, or are impertinent, correction (as the only alternative) must be administered."

Washington badgered Whitting to keep another slave named Gunner hard at work to "continue throwing up brick earth". Gunner was 83 years old.

With his Mount Vernon plantation creaking under financial pressure owing to his long absences serving the country, Washington would fire off angry letters to his overseers insisting on greater crop productivity.

Given these reprimands it is perhaps hardly surprising that another of his estate managers, Hiland Crow, was notorious for brutally flogging slaves.

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In early 1788 the Potomac river froze over for five weeks, but even with nine inches of snow on the ground, Washington did not spare them from gruelling outdoor labour.

He sent the female slaves to dig up tree stumps from a frozen swamp.

During this Arctic snap, Washington ventured to ride out and inspect his farms, but noted in his diary that, "finding the cold disagreeable I returned".

When some of his slaves absconded during the Revolutionary War to find protection - humiliatingly, for him - with the enemy, Washington did not let up in his efforts to reclaim what he saw as his property.

One internal British memo portrayed him after victory as demanding the runaways be returned "with all the grossness and ferocity of a captain of banditti". The British refused.

Whenever George and Martha's bondmen and women did flee, the first couple seemed to regard them as disloyal ingrates.

In one runaway notice Washington posted in a newspaper, he wrote that a slave named Caesar had escaped "without any cause whatever".

That these enslaved human beings might thirst for freedom, or even the opportunity to learn to read and write, did not seem to occur to him.

Professor Joseph Ellis, author of American Sphinx: The Character of Thomas Jefferson, says of the founding fathers: "They could imagine a nation-sized republic, which nobody else had ever done before.

"They could imagine the separation of church and state, which nobody else had ever done before.

"They could imagine a government based on checks and balances that prohibit any form of dictatorship at the presidential level. Nobody had ever done that before.

Image copyright Getty Images Image caption The Jefferson Memorial is one Washington DC's main landmarks

"They could imagine power flowing from the people upwards, rather than from God downward.

"All those unbelievable acts of imagination. The most creative political group in American history. We'll never replicate that.

"But they could not imagine a biracial society."

Jefferson, as every American schoolchild knows, is the nation's third president, and a genius political theoretician who penned arguably the five most important words in modern history - "all men are created equal" - in the 1776 Declaration of Independence.

He also owned up to 140 slaves.

A bon vivant who lived in luxury at a palatial Virginia estate, Jefferson knew America's original sin was a "depravity", as he described it.

But his statements about black people are rarely taught in classrooms today.

Here are some Jefferson quotes that visitors will not find on his memorial, a Roman pantheon-style temple to liberty where the Sage of Monticello's graven image keeps vigil over the Tidal Basin in Washington DC.

To his friend, French social reformer the Duc de La Rochefoucauld-Liancourt, Jefferson confided that he envisaged eventual manumission to entail "exporting to a distance the whole black race".

The duke wrote: "He [Jefferson] bases his opinion on the certain danger… of seeing blood mixed without means of preventing it".

And yet Jefferson, historians say, fathered up to six children by one of his mixed-race slaves, Sally Hemings.

In his book Notes on the State of Virginia, he prophesied a race war in America and "convulsions which will probably never end but on the extermination of the one or the other race".

Jefferson also opined in this work that black people's "unfortunate difference of color" made them less beautiful than whites.

"They are more ardent after their female," he continued, "but love seems with them to be more an eager desire, than a tender delicate mixture of sentiment and sensation.

"Their griefs are transient… in reason much inferior."

And so on.

Media playback is unsupported on your device Media caption What Trump said versus what I saw - by the BBC's Joel Gunter

Professor Ellis believes a plaque should be put up at the Jefferson Memorial to correct the record and admit some of the Declaration author's less savoury statements.

"Jefferson embodies the inherent contradictions, a kind of self-deception, that co-exists in us, too," the biographer said.

"Given the relationship with Hemings, the fact that he refused to take a leadership position on ending slavery because of his fear of miscegenation, it makes his hypocrisy even more dramatic.

"He's got slaves who are his children serving him at dinner. But he doesn't seem to find that troubling. It's mind-boggling."

"Racism is a chromosome in the DNA of the United States," Professor Ellis added. "It's like cancer. It ain't never gonna be cured."

Should Americans therefore disavow these founding fathers as scoundrels and national embarrassments, or accept them as men of their time, demigods with feet of clay, who bore their imperfections even as they sought to steer their country beyond them?

What actually is the difference between monuments to the founding fathers and Confederate leaders?

Dr Clarence Jones - the African-American speechwriter who helped civil rights legend Dr Martin Luther King Jr craft his 1963 "I Have a Dream" address, four words that shaped modern America - explains.

He says: "Sure, George Washington and Thomas Jefferson owned slaves.

"There was no question they were morally compromised in their effort to fashion together this new country, a republic, based on the principles and precepts enshrined in the Declaration of Independence.

"But neither of those two persons led the nation in treasonous insurrection to overthrow the government they had formed in order to preserve the institution of slavery. Period.

"On the contrary, they devoted their life to saving and founding this country."

He says that commemorating the valour of the Confederacy is just as wrong as celebrating the soldiers of the Third Reich.

"What Charlottesville tells us is, it's no longer possible for the United States to ignore this unresolved issue of reconciliation over slavery," said Dr Jones.

"Trump missed an extraordinary opportunity - and he still has it - of exercising the leadership of reconciler and healer-in-chief for the nation today."

Washington and Jefferson are not the only American historical titans who can seem diminished when viewed through the lens of present-day values.

Take Abraham Lincoln, the Great Emancipator and Civil War leader who destroyed the South's slavocracy.

He is immortalised in another neo-classical shrine on the National Mall.

But as Hofstra University history professor Alan Singer points out, the nation's 16th president espoused racist opinions as his political persona evolved.

He is quoted as saying to applause at a debate at Charleston, Illinois, during an 1858 Senate election campaign: "There is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality."

Image copyright Getty Images Image caption Donald Trump and wife Melania at the Lincoln Memorial in January

The Republican leader is also recorded as having tried to persuade a black delegation in 1862 that African-Americans should self-deport and colonise somewhere like Central America, arguing that it would be "extremely selfish" if they refused.

"The United States needs to have a general evaluation of who we are as a nation, so we can come to terms with our present by understanding our past," says Professor Singer.

"Nations need heroes to define who we are, to help us see ourselves in a better light.

"And the United States has heroes. But we tend not to see the warts.

"We tend to try to erase the parts we don't want to see. And this is a time when we have to look."

Sometimes, though, it can be hard to look.

President Lyndon Baines Johnson is lionised as the signer of the 1964 Civil Rights Act - one of the greatest legislative accomplishments of any US administration - which outlawed discrimination.

However, LBJ is also known to have frequently tossed racial slurs around the cloakrooms of the US Senate, according to his biographer Robert Caro.

Johnson nicknamed an earlier iteration of the landmark act for which he is known as "the n***** bill".

In his memoir, Capitol Hill in Black and White, African-American chauffeur Robert Parker relates a disturbing interaction while he was driving for the Texan.

Johnson, he recalls, asked him whether he objected to being called "n*****".

Image copyright Getty Images Image caption President Johnson with civil rights campaigner Martin Luther King Jr

When Parker replied that he would rather be addressed by his own name, Johnson allegedly retorted: "As long as you are black, and you're gonna be black till the day you die, no one's gonna call you by your goddamn name.

"So no matter what you are called, n*****, you just let it roll off your back like water, and you'll make it. Just pretend you're a goddamn piece of furniture."

But Dr Jones believes that LBJ, for all his flaws, understood that his duty as chief magistrate of the United States was to lead his country towards sunlit uplands of a more perfect union, to achieve the unfulfilled promise of its founding.

The University of San Francisco professor is in little doubt what his old friend, Dr Martin Luther King Jr, would say to the current White House incumbent.

"I have no question," says Dr Jones, "that the pre-eminent apostle of love and non-violence in the 20th Century would remind President Trump he has a responsibility to indicate to the nation what is right and what is wrong.

"This is not a time to engage in moral relativity.

"I really believe that President Trump is not beyond redemption, that he still has an opportunity to rise to the majesty of the office."