Donald Trump asked Boris Johnson to help the US attorney-general to undermine the Mueller investigation

President Trump personally contacted Boris Johnson to ask for help as he tried to discredit the Mueller investigation into possible connections between Russia and his 2016 election campaign, The Times understands.

Mr Trump also contacted the leaders of countries including Australia and Ukraine to ask them to help William Barr, his attorney-general, to gather evidence to undermine the investigation into his campaign’s links to Russia.

Robert Mueller, the special counsel, refused to exonerate Mr Trump of wrongdoing when he released his findings in April, prompting the president to set up his own investigation in an effort to prove that the inquiry was politically motivated.

The call to Ukraine’s President Zelensky is the subject of the impeachment inquiry in Congress into whether Mr Trump exploited high-level