A veteran American journalist has described the thought of President Donald Trump being re-elected as "preposterous".

Michael Wolff, author of 2018 book Fire and Fury which documented Trump's chaotic first few months in office, said this while talking about his new book Siege: Trump Under Fire with Mike Hosking on Newstalk ZB.

"One of the things about reporting on the Trump world, it's always nose to the grindstone," Wolff said.

"It doesn't really have any effect other than to keep you working, to keep following this incredible story which changes from moment to moment."

Wolff said things had got "progressively worse" since his first book. His latest documents a White House under pressure by the Mueller investigation and a President who had hardly grown into his role.

"The dominant view is that Donald Trump is a strong man, no attack on him sticks, and he's marching to re-election," he said.

"This narrative is a calamity, the people he came into the White House with all have left, and left with acrimony. The second wave have left with acrimony. More and more, what you have is Donald Trump is a man alone, alone with his daughter and son-in-law."

Wolff said the mid-terms had been catastrophic for Trump, who now faces mounting pressure with investigations, subpoenas and possible impeachment.

"I've always from the beginning looked at this as a train wreck. We're just unclear where the wall is that the train will crash into, but it is there and it will crash."

He described the thought of Trump getting re-elected as preposterous.

"Donald Trump...is not capable of doing the things that a national election requires; all the organisational needs, the requirements that you deal with a lot of people and command their respect and their loyalty, the ability to shape and moderate your message," Wolff said.

"All of these things are well beyond Donald Trump."

Wolff's view was that Trump won the election in 2016 because of his former chief strategist Steve Bannon.

"I do not see anybody, anywhere in Trump world at this point who can bring that kind of intelligence and strategic sense and actual vision to whatever it is that Donald Trump is and represents," he added.

Although Wolff's prediction was for Trump to go the full term, he didn't think he would be back in the White House after the next election.

When asked by Hosking if there will be a third book, Wolff replied: "At this moment in time, I'd say I certainly hope not...but this story is certainly ongoing and it is the story of our lives."