The Republican race for the White House is getting crowded. With eight candidates all gathering in Iowa to campaign, eat roast pork and ride motorbikes, the Americast team looks at who came out on top and whether any of them could beat Donald Trump, who is facing fresh criminal charges over his handling of classified documents.

Harvard professor Steven Pinker, who sees himself as a liberal, tells us why he thinks academic freedom is under threat on US college campuses.

And first, Sarah wanders through the White House with the BBC’s political editor, Chris Mason, who has flown with the prime minister to Washington.

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Find out more about our award-winning “undercover voters” here: bbc.in/3lFddSF.

This episode was made by Daniel Wittenberg, with Alix Pickles, Natasha Fernandes and Alex Collins. The technical producer was Gareth Jones and the sound designer was David Crackles. The editor is Jonathan Aspinwall.