Democrats are hoping that a claim that the FBI is sitting on information about alleged “co-ordination” between Donald Trump’s presidential campaign and the Kremlin will help discredit the agency, led by director James Comey, as biased towards the Republican nominee.

One day after Harry Reid, the Senate minority leader, wrote a letter to Mr Comey demanding he make public “explosive information about close ties and co-ordination between Donald Trump, his top advisors and the Russian government,” others in the party began to weigh in on Monday.

Elijah Cummings, a veteran Congressman from Maryland and the top Democrat on the House Oversight and Government Reform Committee, similarly berated the FBI in a Twitter message. “Members of Congress have asked 4 months 4 the FBI to provide us w/ info as re: Trump and Russian govt. connections,” he wrote.

In his letter, Mr Reid, who is retiring from the Senate after the election, suggested he and other top members of Congress have been hearing for months about possible ties between the Trump campaign and Moscow during closed-door intelligence briefings on Capitol Hill.

The Senator, who has a record of making dramatic claims about his foes without always having the evidence, released the letter on Sunday evening. It came two days after Mr Comey threw a grenade into the race for president revealing his agents had found a whole new cache of emails that may shed light on Hillary Clinton’s use of a private email server when she was Secretary of State.

Armed with a warrant from the courts, investigators were due on Monday to start sifting through the new emails, found on devices co-owned by Huma Abedin, top aide to Hillary Clinton, and her estranged husband, Anthony Weiner. It’s unclear how long the process will take, however.

James Comey's decision drew criticism from Republicans and Democrats (Getty Images)

“Your actions in recent months have demonstrated a disturbing double standard for the treatment of sensitive information, with what appears to be a clear intent to aid one political party over another,” Mr Reid told Mr Comey, adding, “You may have broken the law” – a reference to the Hatch Act that bans public officials from trying to influence elections.

But it was his suggestion that the FBI had failed to share information regarding Camp Trump and Russia with the public that was drawing most attention on Monday.

“In my communications with you and other top officials in the national security community, it has become clear that you possess explosive information about close ties and co-ordination between Donald Trump, his top advisors and the Russian government — a foreign interest openly hostile to the United States, which Mr Trump praises at every opportunity,” Mr Reid wrote to Mr Comey.

There was no official explanation from Mr Reid or his office on exactly what he was referring to. “There have been classified briefings on this topic," his spokesman, Adam Jentleson, told The Hill. "That is all I can say.”

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Earlier this summer, Mr Reid wrote to Mr Comey asking that he investigate Carter Page, a New York banker, whom Mr Trump first named as one of his campaign’s foreign policy advisors last March, in part for his considerable Russian expertise. Specifically, the Senator suggested he had travelled to Moscow in July, delivered a graduation speech at the New Economic School and then met officials close to Russian President Vladimir Putin.

Separately, Yahoo News, citing a “well-placed Western intelligence source”, said last month that the US government had received intelligence that Mr Page met Igor Sechin, a friend of President Putin who runs Russian oil giant Rosneft, and Igor Diveykin, a high-ranking Russian intelligence official and that he may have conducted “talks about the possible lifting of economic sanctions if the Republican nominee becomes president”.

Last month, Mr Page told The Washington Post he was taking a leave of absence from the Trump campaign after being attacked by Democrats, including by Mr Reid. “All of these accusations are just complete garbage,” Mr Page said of the allegations at the time.

Also, Mr Trump’s former campaign manager, Paul Manafort, resigned from this team this summer in the wake of reports of his past business dealings with the former president of Ukraine, Viktor Yanukovych, an ally of Mr Putin.

“The FBI now potentially faces a very serious credibility problem,” Mr Cummings told The Daily Beast. “If it turns out that the FBI is in fact investigating – or planning to investigate – Paul Manafort because of his dealings with Russia, or anyone else associated with Donald Trump and does not disclose these facts to the American people before the election, then the FBI will be accused of a double standard when those facts ultimately do come out.”

Democrats have accused Mr Trump of cosying up to Mr Putin, whom he has termed a stronger leader than Barack Obama. Yet he has repeatedly insisted that he does not know Mr Putin and has no relationship with him or with the Russian government and has no investments in Russia.

Even so, in the last television debate, Ms Clinton directly accused him of being Mr Putin's “puppet”, an allegation he aggressively refuted. Multiple US intelligence agencies have concluded that Russian hackers were behind intrusions into the email history of the Democratic National Committee raising the notion that Russia has been directly meddling in the US election.