A lawyer for Hillary Clinton's 2016 presidential campaign lied to the FBI to "manipulate" the agency in order to win the election, a court has heard.
Arguments in the trial of Michael Sussmann have begun with prosecutors saying he hoped to create an "October surprise" in the race's final weeks.
Mr Sussmann has pleaded not guilty.
He is the first defendant to go on trial in an investigation into the FBI's original probe to find if Donald Trump was conspiring with Russia.
The charges arise from a meeting between Mr Sussmann, a cyber-security lawyer, and an FBI agent in 2016.
Mr Sussmann presented what he claimed was evidence of suspicious internet traffic connecting the Trump Organization to Russia's Alfa Bank. The FBI looked into the allegation and found nothing suspicious.
Prosecutors say Mr Sussmann lied by not disclosing in the meeting that he was working for the Democrat's campaign. The indictment charges that he claimed not to be representing any particular client and that he presented himself purely as a concerned citizen.
A lawyer for Mr Sussmann denounced the trial as an "injustice" at Tuesday's hearing in a Washington DC federal courthouse.
Mr Sussmann is being charged by US Department of Justice Special Counsel John Durham, who was picked by the attorney general under President Trump in 2019 to investigate FBI misconduct in the original Trump-Russia investigation by Special Counsel Robert Mueller.
The Mueller inquiry concluded in 2019 that it could find no evidence of any criminal conspiracy between the Trump campaign and Russia, though it did determine Russia had sought to help Mr Trump win.
President Trump always said the Mueller inquiry was biased against him.
In court on Tuesday, prosecutor Brittain Shaw argued that Mr Sussmann had hoped to drop a bombshell in the final days of the November 2016 race.
"This case was about privilege," Ms Shaw said, describing the defendant as a "high-powered DC lawyer".
Lawyers for Mr Sussmann called the government's argument "nonsensical", arguing that the FBI would have known he had represented the Democratic National Committee earlier that year after their computer servers were hacked.