Michael Sussmann is accused of misleading the FBI during a September 2016 meeting by telling the bureau's top lawyer that he was not acting on behalf of a particular client when he presented computer data that he said might connect the Russian government to then-candidate Donald Trump.
In reality, prosecutors say, he was acting on behalf of the Clinton campaign and another client who had provided him with the data.
He lied, prosecutors told the jury, in hopes of generating an "October surprise" of FBI investigations into Trump and negative news coverage of him, and because he knew the FBI would consider the information less credible if it thought it was being presented on behalf of the Clinton campaign.
"He told a lie that was designed to achieve a political end, a lie that was designed to inject the FBI into a presidential election," prosecutor Brittain Shaw said.
But Sussmann's lawyers sought to counter each of the prosecution's allegations, presenting him as a well-respected attorney with deep experience in law enforcement intelligence matters who never lied to the FBI and never would.
The fact that he represented Democratic clients was well-known to the FBI and not anything he intended to hide.
"He was someone the FBI knew represented partisan clients," defence lawyer Michael Bosworth said in his opening statement.
"The FBI knew that he represented the Clinton campaign that summer. The FBI knew that he was an attorney for the DNC, the Democratic Party itself."
In any event, Bosworth said, it would be impossible for prosecutors to prove that Sussmann had lied because only he and the FBI lawyer he met with, James Baker, were present and neither took notes.
Five and a half years after the meeting, Baker's memory of what was said is "clear as mud," Bosworth said.
Sussmann's trial is the first arising from special counsel John Durham's investigation into the FBI's original probe into alleged Russian government election interference and potential ties with the Trump campaign.
Though Durham was thought to be focused at least initially on misconduct by government officials during the course of the Russia investigation, the Sussmann case alleges wrongdoing by a tipster to the FBI rather than the FBI itself.
In an early recognition of the politically loaded nature of the case, Shaw urged jurors to put aside any feelings they might have about Trump, Russia or Clinton.
"Some people have very strong feelings about politics and Russia, and many people have strong feelings about Donald Trump and Russia. But we are not here because these allegations involved either of them, nor are we here because the client was the Hillary Clinton campaign," Shaw said.
Rather, she added, "We are here because the FBI is our institution. It should not be used as a political tool."
At issue is a September 19, 2016 meeting in which Sussmann presented Baker, the FBI's then general counsel, with computer data gathered by another of his clients that purported to show furtive contact between computer servers of the Trump Organization and Russia-based Alfa Bank.
That connection, if true, would have been explosive at a time when the FBI was examining whether the Trump campaign and the Russian government were conspiring to sway the election.
The FBI did investigate the data but found nothing nefarious and the communication instead reflected what Shaw described as a "spam email server" used to send out marketing.
"The server did not reflect a crime," Shaw told jurors, "nor was it a threat to national security".
