Almost two-thirds (64 per cent) of Americans believe that Donald Trump pressuring the leader of Ukraine to investigate his potential 2020 presidential rival is a serious issue, according to a new poll.

A total of 43 per cent of respondents to the ABC/Ipsos survey said the allegations were “very serious” while 21 per cent agreed the situation was at least “somewhat serious".

Just 17 per cent said that they were surprised by the allegations against the US president, which were detailed in a whistleblower complaint and backed up by a transcript released by the White House itself.

It has emerged that days after ordering a freeze to some military assistance for Ukraine, on 25 July, the US president pressed his Ukrainian counterpart Volodymyr Zelensky, to work with Rudy Giuliani, his personal lawyer and US attorney general William Barr to investigate leading Democratic presidential candidate Joe Biden and his son Hunter.

Hunter Biden was a board member Burisma, a Ukrainian natural gas company and Mr Trump has alleged that Mr Biden pressed for the sacking of Ukrainian prosecutor Viktor Shokin in 2016 to protect the business.

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While serving as vice president and leading the Obama administration’s diplomatic dealings with Kiev, Mr Biden did call for Mr Shokin to be removed from his post. He also threatened to withhold $1bn (£813m) in aid to Ukraine.

But he was one of a number of western officials who saw Mr Shokin as a hindrance to anti-corruption investigations and there is no suggestion of impropriety on behalf of either Mr Biden or his son.

After details of Mr Trump's call emerged, formal impeachment proceedings were launched against him by Nancy Pelosi, the speaker of the House.

The senior Democrat had previously been hesitant to put her weight behind such an investigation.

But she said that the allegations that he attempted to use US taxpayer money to force a foreign government to investigate Mr Biden - a leading Democratic candidate for the party’s 2020 presidential nomination - had crossed a line.

Mr Trump himself, has sought to characterise the impeachment inquiry launched by his Democrat rivals after the allegations emerged, as “lawless”, although "multiple US government officials" indicated that the president had attempted to coerce the investigation during a 25 July phone call.

He said that it was an attempt by his political rivals to tarnish his presidential legacy will backfire during 2020 presidential election.

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“Will happen to all of those seeking unlawful impeachment in 50 Trump type Districts. We will win big!” Mr Trump tweeted, agreeing with a statement from Republican National Committee chairwoman Ronna McDaniel, who suggested that swing district voters are not interested in the numerous corruption and law breaking against the US leader.