A former Trump campaign aide arrived Friday at the federal courthouse in Washington for a scheduled grand jury appearance days after he defiantly insisted in a series of news interviews that he intended to defy a subpoena in special counsel Robert Mueller's Russia investigation.

Sam Nunberg did not respond to reporters' questions as he entered court shortly after 9 a.m.

Nunberg on Monday had balked at complying with a subpoena that sought his appearance before a grand jury as well as correspondence with multiple other campaign officials.

But later that night, Nunberg told The Associated Press that he had relented and would wind up complying after all. He said he had worked for hours to produce the thousands of emails and other communications requested by Mueller, who is investigating whether the Trump campaign improperly co-ordinated with Russia during the 2016 presidential election.

"I thought it was a teachable moment," he said of his 24 hours in the limelight.

Nunberg was among the earliest advisers to Trump when the billionaire and reality TV host plotted a presidential bid but was in and out of the campaign, leaving for good in the summer of 2015 when racially charged Facebook posts from years earlier were discovered.

So far, 19 people and three companies have been charged in Mueller's investigation. Among them are Trump's former campaign chairman and the former White House national security adviser. Five people have pleaded guilty.