Donald Trump will lose after failing to follow Mitt Romney - Expert

Any chance of the Republican Party regaining the White House has been hampered by Donald Trump's campaign tactics, according to one U.S. policy expert.

The latest and final poll from NBC and the Wall Street Journal shows Clinton holding a slim lead over Trump, with a four-way race showing her on 44 percent to Trump's 40 percent.

James Boys, senior US policy expert and associate professor of international political studies at Richmond University, told CNBC Monday that Trump is not waging a campaign that can win the election.

"If you put in someone who could reach out to Hispanics, to women, to the African American community and build on what Mitt Romney had done four years ago, maybe.

"But when you see him do the exact opposite, it is impossible to see how he can win this," he said.

On the news that the FBI has found no criminality in its latest probe in to emails connected to the private server of Hillary Clinton, Boys said it was questionable how much of a boost the Democratic campaign could receive at such a late stage.

But he claimed early voting appeared to favor Clinton.

"There has been a huge move for early voting; anywhere of up 30-40 percent of votes have already cast.

"The turnout seems to be pretty good, especially among the Hispanic community," he said.

Boys described fears that polls could be wrong as they were during the British referendum on EU membership as an "all too simplistic parallel".

He said it was important to consider the sheer volume of U.S. election polls being conducted on a daily basis.

And on what states to look for tomorrow evening, Boys said the state of Florida once again holds the key.

"Quite frankly it's very, very close. If Clinton wins it then she's president, if not then we could be in for a long night," he said.