A poll conducted by ABC suggests the majority of Americans are unwilling to support President Donald Trump in the 2020 election, with healthcare and immigration policy cited as major deciding factors.

Released Monday, the poll found 55 per cent of those polled refuse to vote for Mr Trump in 2020, with 40 per cent opposing his re-election based on his handling of healthcare. On immigration, 44 per cent oppose a second term for the president, while 31 per cent support it.

A majority of Americans polled - 58 per cent - also believe Mr Trump lied to the public about the Mueller investigation.

The poll shows that this thinking may have a considerable impact, with 36 per cent of those polled citing the Mueller report, an edited version of which was released to the public on 18 April, making them likely to oppose Trump in 2020.

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Intended turnout meanwhile appeared "remarkably" high, with 75 per cent of Americans, including 85 per cent of registered voters, saying they are "certain" to vote in the election.

The news agency noted that if that level is maintained, it could boost Democratic candidates, many of whose core support groups are "less reliable voters".

Also notably, support among Mr Trump’s own party showed a slight decrease in the poll - 15 per cent of Republicans said they would "definitely not" support the president’s re-election, with 30 per cent of those identifying as conservative polling the same way.