Among the exchanges between Donald Trump and Joe Biden at last night's presidential debate, one in particular caught the public's imagination. On the hotly contested issue of US race relations, President Trump made a reference to Abraham Lincoln - the 16th US president whose victory in the Civil War secured the abolition of slavery. Mr Biden sought to capitalise on the apparent comparison with a mocking quip, but Mr Trump didn't find it funny. It went like this: President Trump asserted - not for the first time - that "nobody has done more for the black community than Donald Trump... with the exception of Abraham Lincoln". He added: "I'm the least racist person in this room." Mr Biden responded: "'Abraham Lincoln' here is one of the most racist presidents we've had in modern history. He pours fuel on every single racist fire. Every single one." Trump: "He made a reference to Abraham Lincoln, where did that come in?" Biden: "You said you're Abraham Lincoln." Trump: "No, no. ... I didn't say 'I'm Abraham Lincoln'. I said, 'Not since Abraham Lincoln has anybody done what I've done for the black community'." Mr Trump hit back by questioning Mr Biden's own record on race issues. He cited the 1994 crime bill that Mr Biden helped to draft and which the Black Lives Matter movement blames for the mass incarceration of African-Americans. The exchange brought swift reaction on social media. Analysts have taken issue with his claims, saying other presidents in modern times have made far greater progress with civil rights, particularly Lyndon B Johnson, who oversaw the Voting Rights Act, the Civil Rights Act and the Fair Housing Act in the 1960s. Last year, Mr Trump made another comparison with the 16th president, saying that no other US leader had been treated as badly by the press as he had - not even Lincoln. "Abraham Lincoln was treated supposedly very badly, but nobody's been treated badly like me," he said. President Lincoln led the Union to victory over the secessionist southern Confederacy in the war of 1861-65. He ordered African-American slaves to be freed in 1863. Just days after General Robert E Lee surrendered in 1865, Lincoln was assassinated at a theatre in Washington DC by John Wilkes Booth, while attending a play.