Joe Biden mistakes Theresa May for Margaret Thatcher. Again.

Democratic 2020 presidential front-runner Joe Biden has cut an impressive figure in the aftermath of last weekend's twin mass shootings, leading the condemnation of Donald Trump and holding the president accountable for his racist and divisive rhetoric.

On Wednesday, Biden told a rally in Burlington, Iowa, that Trump had "has fanned the flames of white supremacy", alluding to the white nationalist manifesto posted on 8chan by the El Paso shooter, 21-year-old Patrick Crusius, who killed 22 people at a Walmart in the city's Cielo Vista Mall.

Barack Obama's former vice-president asked his supporters:

How far is it from Trump's saying this 'is an invasion' to the shooter in El Paso declaring his attack is a response to 'the Hispanic invasion of Texas?' Not far at all.

How far is it from the white supremacists and neo-Nazis in Charlottesville - Trump’s 'very fine people,' chanting 'You will not replace us' - to the shooter at the Tree of Life synagogue in Pittsburgh saying Jews 'were committing genocide to his people?' Not far at all.

In both clear language and in code, this president has fanned the flames of white supremacy in this nation.

As powerful as that address was, Biden is known to be gaffe-prone and made an unfortunate slip of the tongue when he told the Asian & Latino Coalition PAC in Des Moines on Thursday that:

Poor kids are just as bright and just as talented as white kids.

He presumably just meant to say "rich" there but it was an embarrassing error indeed.

More bizarrely, while speaking at the Iowa State Fair, Biden managed to confuse Britain's recently-ousted prime minister Theresa May with her Conservative ancestor, Margaret Thatcher, the second time he has made that same blunder.

Speaking to his audience about Trump's reaction to the violence at the Charlottesville "Unite the Right" rally of August 2017 - in which an Antifa activist was killed - the 76-year-old candidate said:

[His words] stunned the nation, and I would argue - I know - shocked the world. International leaders spoke to me about it.

You had people like Margaret Tha... excuse me. You had people like the former chairman and the leader in the... in Germany.  You had Angela Merkel stand up and say how terrible it was.

International leaders looked at us like what in God's name is happening to the United States of America?

Realising his mistake, Biden stopped himself short, stuttered and quickly changed tack to talk about her German counterpart rather than Mrs May.

He did the same thing three months ago, telling a campaign rally in South Carolina back in May he had received a phone call from Thatcher complaining about Trump - despite the Iron Lady having died in 2013.

He stumbled on:

One I can say [the name of] is Margaret Thatcher - um, excuse me, Margaret Thatcher, Freudian slip. But I knew her too…the prime minister of Great Britain, Theresa May.

While these moments of confusion are understandable for a veteran public speaker in the global spotlight, Biden will need to cut out avoidable self-owns like this before President Trump's disparaging "Sleepy Joe" taunt starts to stick.

More: Joe Biden says Trump 'has fanned the flames of white supremacy'