Voters in battleground states will need to overwhelmingly swing in his favour and Mr Trump will have to win back crucial voting blocs to secure victory, they said.
It is likely his turnout will also need to dramatically outperform Democrat rival Joe Biden’s on account of ballots already cast.
Whit Ayres a veteran Republican pollster, said: “In 2016, his chances of winning the election were those of drawing an inside straight in poker.
“The question this year is whether he can draw an inside straight two hands in a row.
It is theoretically possible but practically difficult
“It is theoretically possible but practically difficult," Mr Ayres said.
While Mr Trump has multiple roads to victory, his most likely route hinges on winning two crucial battleground states – Florida and Pennsylvania.
If he can claim both and hold on to other Sun Belt states he narrowly carried in 2016 – North Carolina and Arizona – while playing defence in Georgia and Ohio, which he won handily in 2016 but where Mr Biden is now competitive, he will win.
Mr Trump’s campaign is also continuing to pour time and money into Wisconsin and Michigan, long-time Democratic strongholds he flipped his way by the slimmest of margins four years ago, while trying to defend Iowa and Maine’s second congressional district and grab Nevada and Minnesota, two states his 2016 rival Hillary Clinton narrowly won.
“We feel better about our pathway to victory right now than we have at any point in the campaign this year,” Mr Trump’s campaign manager, Bill Stepien, told staff on a conference call this week.
“And this optimism is based on numbers and data – not feel, not sense.”
But polling shows Mr Trump trailing or closely matched in nearly every state he needs to win to reach 270 Electoral College votes.
Paul Maslin, a long-time Democratic pollster, said barring some kind of major upset, the president needs to hold on to at least one of the three rustbelt states he won in 2016 – Pennsylvania Wisconsin or Michigan.
“I don’t see any other way for Trump to do this,” he said.
Fox News polls released on Wednesday show Mr Biden with a clear advantage in Michigan and a slight one in Wisconsin.
In Pennsylvania, recent polls show Mr Biden ahead but vary on the size of his lead.
For all of that, though, Mr Trump’s team can draw comfort from this historical footnote – in all three states, Mrs Clinton led in the polls in the final weeks of 2016.
But the president’s “fundamental problem”, according to Mr Ayres, “is that a large number of states that he won comfortably last time” are currently close.
With 29 electoral votes, Florida is arguably the most crucial state for Mr Trump – a loss there would make it nearly impossible for him to retain the White House.
But the state, which has sided with the winner of nearly every presidential race for decades, is also known for razor-tight elections – most notably in 2000 when George W Bush defeated Al Gore by 537 votes after a recount.
While polling early this month showed Mr Biden with a slight advantage, two recent polls have the two candidates neck-and-neck.
In 2016, Mrs Clinton won more votes in the state than Barack Obama in both his races, with commanding leads in Democratic strongholds like Miami-Dade.
But Mr Trump ran up the the score with stunning turnout in smaller counties, including across the Florida Panhandle.
His campaign expects do even better this time due to a robust turnout operation.
Republicans say they have registered 146,000 more voters than Democrats since the pandemic hit in March.
Democrats, meanwhile, hope to triumph when it comes to early voting and voting by mail.
It is a similar story in Pennsylvania, where two recent polls show Mr Biden maintaining a clear lead and another suggesting a narrow one.
Mr Trump won the state by just over 44,000 votes last time, powered by an overwhelming showing in rural areas and small towns and cities.