Roger Stone undermined the effectiveness of the congressional investigation into Russian tampering in the 2016 election by repeatedly and deliberately lying under oath, prosecutors told jurors in closing arguments Wednesday.

A veteran Republican political operative and longtime confidant of Donald Trump, Stone is accused of lying to lawmakers about his attempts to communicate with the anti-secrecy website WikiLeaks, tampering with witnesses and obstructing a House Intelligence Committee investigation into whether the Trump presidential campaign coordinated with Russia to tip the 2016 election.

He has denied wrongdoing.

Prosecutor Jonathan Kravis said Stone lied to protect the Trump campaign. Several witnesses have highlighted how Trump campaign associates were eager to take advantage of the more than 19,000 emails that had been hacked by Russia from the Democratic National Committee and were being released in batches by WikiLeaks.

Steve Bannon, who served as the campaign’s chief executive, testified that Stone had boasted about his ties to WikiLeaks and its founder Julian Assange, alerting them to pending new batches of damaging emails. Campaign officials saw Stone as the “access point” to WikiLeaks, he said.

As a result, the campaign looked to Stone to make contact with WikiLeaks and learn more about the content and timing up of the upcoming email releases.

“Roger Stone knew that if this information came out, it would look really bad before his longtime friend Donald Trump, so he lied to the committee,” Kravis said. “He not only tried but succeeded in impeding the committee’s investigation.”

Stone was indicted in January as part of special counsel Robert Mueller’s investigation into Russian electoral tampering.