The seventh in a series of debates to determine the Democratic challenger to Donald Trump has the fewest participants yet.

Six contenders will take to the stage in Iowa – just weeks before the state’s caucuses – and for the first time in this set of debates, none of the candidates will be people of colour.

Entrepreneur Andrew Yang, who was in last month’s debate, did not make the cut, leaving an all-white field.

New Jersey Senator Cory Booker, who was the only black candidate remaining who had made a previous debate, ended his campaign on Monday, saying “there was no longer a path to victory”. Deval Patrick is now the only black presidential candidate left.

The debate comes as recent polls show former Vice President Joe Biden, Vermont Senator Bernie Sanders, Massachusetts Senator Elizabeth Warren and former South Bend mayor Pete Buttigieg leading the pack.

Foreign policy is expected to be in focus, as this is the first debate since President Trump’s controversial killing of Iranian general Qassem Soleimani.

Viewers should expect questions about an ongoing row between Senators Sanders and Warren concerning an alleged conversation in which he is said to have told her that a woman cannot win the election. A statement from the Warren campaign stressed unity between the two Democrats who are seen to represent the left wing of the party. All the same, supporters of both campaigns have continued to fight on Twitter since the story first broke.

The debate also falls on the eve of a key House vote on whether to send articles of impeachment against Donald Trump to the Senate, which Nancy Pelosi announced today.