FBI Director James Comey could spark a political firestorm on Monday when he publicly testifies about Russian meddling in the 2016 presidential election and - crucially - whether there is any evidence that Trump aides colluded with the Kremlin.
Mr Comey will also be pressured to clarify, once and for all, President Trump's explosive allegation that former President Barack Obama spied on him in the run-up to last November’s election.
The FBI director’s highly-anticipated appearance before the House Intelligence Committee, which is investigating Russian activities during the campaign, could have significant implications for Mr Trump’s presidency.
Mr Trump has been plagued by persistent questions over contacts between his closest associates and Russian officials at a time when the US intelligence community believes Russia was aggressively working to thwart Hillary Clinton and sway the election in his favour.
The president has dismissed any suggestion that his campaign conspired with Moscow as "fake news" peddled by his political opponents still bitter about his victory last November.
But the continuous flow of revelations about how members of the Trump inner circle have had connections or interactions with Russian officials have only fuelled the intrigue and suspicion.
The president’s critics hope Mr Comey can strike a lasting blow by revealing evidence of illicit activity or at least the existence of a criminal investigation into alleged Trump-Russia ties; weary members of his own party hope the FBI director can finally dispel the theory to enable Mr Trump to get on with the process of governing.
Mr Comey may not be as forthcoming with fresh information as both Republicans and Democrats would like due to the FBI’s policy on not commenting on active and ongoing investigations.
But the FBI director, who is no stranger to controversy, is still likely to upset someone by the end of the three-hour hearing.
If Mr Comey publicly refutes Mr Trump’s assertion that Barack Obama ordered a wiretap of Trump Tower - which he is widely expected to do - he will inevitably incur the president’s wrath.
If he remains silent on the key questions surrounding alleged collusion, Mr Comey will leave himself open to accusations of hypocrisy and bias by Democrats who say he was more than willing to discuss Hillary Clinton’s private email server eleven days before polling day.
Mr Comey’s testimony promises to be a fascinating watch - but it could leave more questions than answers on a saga that just will not go away for President Trump.