WASHINGTON (BLOOMBERG) - United States President Donald Trump announced he has authorised the declassification of documents related to the Federal Bureau of Investigation's (FBI) Russia investigation and the probe into Mrs Hillary Clinton's use of a private e-mail account, part of his efforts to cast aspersions on his political enemies as he falls further behind in his bid for re-election.

"I have fully authorised the total Declassification of any & all documents pertaining to the single greatest political CRIME in American History, the Russia Hoax," Mr Trump tweeted on Tuesday (Oct 6).

"Likewise, the Hillary Clinton Email Scandal. No redactions!" Mr Trump said.

Former FBI director James Comey told a Senate committee last week that the inquiry into whether people close to Mr Trump conspired with Russia to interfere in the 2016 election was largely conducted "by the book", but that specific aspects of the inquiry fell short.

Pressed by Senate Judiciary chairman Lindsey Graham, who said the probe was based on faulty assumptions and evidence tampering, Mr Comey said he found the shortcomings - which included doctoring an e-mail from the Central Intelligence Agency - "deeply disturbing".

But he backed an inspector-general's report that concluded the probe was valid and not driven by bias in the bureau's leadership.

Senate Republicans are trying to put the spotlight back on what they said was a politically motivated probe meant to undermine Mr Trump's candidacy in 2016 and, later, his presidency.

The debate comes after US intelligence agencies have once again assessed that Russia is interfering again in the 2020 presidential race to aid Mr Trump by denigrating his rival, former vice-president Joe Biden.

Mr Trump has said US officials should be more focused on China, not Russia.