There has been talk of impeaching US president Donald Trump since he was first elected back in 2016, but the wheels began to move in earnest over the past week.It all centres around a whistleblower revealing details of a call last July between Trump and Ukrainian President Volodymyr Zelensky. A 'favour' was requested, one which could amount to interference in the 2020 election campaign.This was enough to spark impeachment proceedings, launched by by US Democrat and speaker of the House of Representatives Nancy Pelosi.But what happens next?