Republican presidential candidate Donald Trump’s run for the White House has hit another hurdle after reports his business organisation may have used a secret email server to communicate with a Russian bank linked to Vladimir Putin.

Mr Trump’s ties to Moscow have long raised eyebrows and provided fodder for his Democrat opponent Hillary Clinton, but he has continued to deny any links throughout this election campaign.

The report published by Slate claimed there was a sustained relationship between a server registered to the Trump Organisation and two servers registered to an entity called Alfa Bank – the largest private commercial bank in Russia.

It added that conversations between the Trump Organisation and Alfa Bank were first logged several months ago, and the servers followed the “contours of political happenings” in the United States.

John Barron, co-host of the ABC’s Planet America, said news of Mr Trump’s connection to Russia was interesting, because it added to a “significant body of evidence that shows there are deep ties between Trump and Russian oligarchs that have been providing a lot of his financing in recent years”.

He said Russia’s financial support of Trump, his former campaign chairman Paul Manafort’s ties to Russian factions within Ukrainian politics and connection to a hack attack on the Democrats show “Russia is working to further the interests of Trump”.

“It doesn’t provide a smoking gun but it helps to build a picture of potentially secretive and nefarious links between the Trump campaign and Russia,” Mr Barron said.

The server “was set to accept only incoming communication from a very small handful of IP addresses”, the report claimed, adding that among those, two Alfa Bank servers accounted for 87 per cent of the Domain Name System (DNS) lookups.

Trump camp denies ‘secret server’ claims

However, Mr Trump’s campaign press secretary Hope Hicks denied the claim.

“First of all, it’s not a secret server. The email server, set up for marketing purposes and operated by a third-party, has not been used since 2010. The current traffic on the server from Alpha bank’s [sic] IP address is regular DNS server traffic – not email traffic,” she said.

“To be clear, The Trump Organisation is not sending or receiving any communications from this email server.

“The Trump Organisation has no communication or relationship with this entity or any Russian entity.”

Meanwhile, the Clinton camp was quick to pounce on Mr Trump’s possible connection to Russia.

It declared the story proof of “the most direct link yet between Donald Trump and Moscow”.

Bad timing

Mr Trump was rapidly gaining ground on his opponent before this latest scandal broke.

According to a RealClearPolitics average of national polls in the US, the aggregator shows him within 3.2 points of Mrs Clinton – who led by 7.1 points on October 18.

It remains to be seen if the claims of a Russian connection will derail his improving poll statistics.

A top aide to Hillary Clinton, Democrat campaign manager Robby Mook, has urged the FBI to disclose what it knows about any such ties, accusing the law enforcement agency of unfairly publicising its inquiry into Clinton’s email practices while staying quiet about Trump.

“If you’re in the business of releasing information about investigations on presidential candidates, release everything you have on Donald Trump. Release the information on his connections to the Russians,” Mook said on CNN.

‘An error of Brexit proportions’

Mr Trump had been making headway into Mrs Clinton’s advantage before the FBI announced on Friday it was reopening an investigation into her use of a private email server while secretary of state.

According to the ABC and The Washington Post poll, the Republican candidate trailed by 12 points at the start of last week at 38-50 behind Mrs Clinton – by Thursday he was within two points at 45-47.

However, Mr Barron said it would take an error of “Brexit proportions” for Mr Trump to win despite his surge.

“Historically no candidate has come back from a six-point deficit three weeks out from an election,” he said.

“It would take an error of Brexit proportions in some of the polling averages [for Mr Trump to win] … and it will take the reactivation of older white voters who maybe haven’t voted for 10-15 years to suddenly get excited and reregister to vote.

“The Trump campaign hopes there’s this hidden white vote that is just out there waiting to be activated but there hasn’t been much evidence to suggest this.

“They didn’t come out in the primaries for him, whether they come out for him come November 8 we’ll just have to wait and see – but it seems unlikely.”

Trump’s dubious accounting

Throughout the presidential campaign, Mr Trump has bragged about how he didn’t pay federal income taxes for years – but his “smart” move may be legally dubious.

The New York Times has acquired documents from the 1990s, showing Mr Trump avoided reporting hundreds of millions of dollars in tax.

After a venture to build a casino empire in Atlantic City failed, Mr Trump asked financial backers to forgive hundreds of millions of dollars in debt he could not repay.

This allowed Mr Trump to avoid reporting any of that canceled debt to the Internal Revenue Service.

The document below show Mr Trump’s lawyers warning him about his tax avoidance manoeuvres in the 1990s.