Inside the Jefferson memorial, a number of texts were inscribed, including three about slavery: "I tremble for my country when I reflect that God is just, that his justice cannot sleep forever. Commerce between master and slave is despotism. Nothing is more certainly written in the book of fate than that these people are to be free."
The last sentence, taken from Jefferson's Autobiography, is incomplete. It continues, as Conor Cruise O'Brien points out, to state that "Nor is it less certain that the two races, equally free, cannot live in the same government. Native habit, opinion has drawn indelible lines of distinction between them."
The suppression of the second half is only a detail in the long campaign to conceal the awkward fact that the imperishable author of the ringing declaration that all men were created equal was not only a slave-owner but also a racist.
Nor can this be brushed aside with the defence that he only reflected the prejudices of his time. George Washington did not share Jefferson's racism. Jefferson believed, as Washington did not, that there was no future for black people in the United States and he therefore advocated that. freed slaves should be sent "back where they came from", in the phrase beloved of modern British racists.
The evidence O'Brien deploys has been painstakingly accumulated by a whole younger generation of American historians. It includes the fact that Jefferson tried to write into the laws of Virginia two proposals that were too strong even for his fellow-slave-owners. One would have made it illegal for free Negroes to enter the state, or to stay there once freed. The other would have removed from "the protection of the laws" any white woman who bore a black man's child: an invitation to lynching.
Thanks to earlier southern historians, it is widely believed that Jefferson, although a slave-owner, wanted to abolish slavery. He did condemn slavery, and no doubt he hated it, if only because of the contradiction between his ideology of liberty and the reality of his life. But he went to great lengths to recapture and punish his own runaways.
Unlike Washington, he did not free his own slaves in his will, with the exception of four who were probably his own children. O'Brien accepts that we shall not know for certain whether Jefferson was the father of Beverley, Harriet, Madison and Eston Hemings, the children of his servant Sally Hemings, until DNA testing has been carried out on their remains. The guardians of the Jefferson cult have always poured scorn on the tale that Sally was Jefferson's mistress. But what is not in doubt is that Sally was the half-sister of Jefferson's own wife, daughter of a liaison between Martha Jefferson's father and a slave.
It is not the chief purpose of O'Brien's book to portray Jefferson as a racist or a hypocrite. Its theme is his role as the principal champion in America of the French Revolution. Although generations of Jeffersonians have portrayed their hero as a pillar of an American democratic tradition far removed from the ferocity of Robespierre, O'Brien notes that Jefferson continued to defend the atrocities in France. After the king's execution, Jefferson as Secretary of State wrote to his charge d'affaires in Paris that "were there but an Adam and an Eve left in every country, and left free, it would be better than as it now is".
Not until long after the Terror did Jefferson condemn the Revolution. And then, suggests O'Brien, one significant factor was Robespierre's proposal, in response to the slave rebellion in Haiti, to emancipate the slaves in all French and British colonies.
"How is it", Dr Johnson asked, "that we hear the loudest yelps for liberty from the drivers of negroes?" The remark has usually been dismissed as a cheap shot from a resentful Tory. But O'Brien suggests there may indeed have been a connection between the cult of Liberty in Virginia and slavery. Liberty to white Virginians included the liberty to own slaves.
Nothing can now change the fact, he believes, that the US will increasingly be a multi-racial society. The mainstream will therefore soon eject Jefferson from the American trinity. He will be left to that minority who defend white supremacy and States' Rights. Both suspects in the Oklahoma City bombing claimed him as an inspiration. Timothy McVeigh, when arrested, was wearing a T-shirt inscribed "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants."
The traditional view of Jefferson is that he was a passionate advocate of liberty for all trapped in the position of owning slaves. O'Brien brings to Jefferson his suspicion of the harm done by revolutionary rhetoric in Ireland and his sympathy for Edmund Burke's negative view of the French Revolution. Making allowance for that, he has put the torch of his persuasive gifts to the evidence heaped up by revisionist historians. Together they have scorched the marble statesman of the Tidal Basin. The questions about Jefferson's ideological legacy raise questions about the nature of US civil religion - and the extent to which it extends its offer of equality to those who are not white North Americans.