Former Trump campaign manager Corey Lewandowski returned to Capitol Hill Thursday for a closed-door interview with the House Intelligence Committee's Russia investigation, sitting with lawmakers for three hours and telling reporters he answered "every relevant question you could imagine."
But Rep. Adam Schiff, D-Calif., the top Democrat on the panel, told reporters that Lewandowski declined to answer some questions relevant to the committee's investigation into allegations of collusion between the Trump campaign and Russia, and Schiff said he had asked Republicans to issue a subpoena to compel Lewandowski to answer questions about the firing of former FBI Director James Comey and discussions he may have had with President Trump about special counsel Robert Mueller.
"Witnesses don't get to pick and choose when it comes to very relevant testimony in regards to our investigation," Schiff said.
Leaving Capitol Hill Thursday, Lewandowski said his committee interview was a waste of time.
"I could be doing something more productive with my life," he said. "There was no collusion, no cooperation, no coordination. Fact"
Lewandowski returned to a House Intelligence Committee that has grown increasingly divided over the direction of its investigation, and whether to keep going at all.
"We're at the point where there's really not much more that we can ask," Rep. Chris Stewart, R-Utah, a member of the committee, told ABC News. "We feel we have an obligation to report at least what we know now."
Democrats remain hopeful there will still be opportunities to learn from key players in Trump's campaign. Schiff said Thursday that Democrat want to question Stephen Miller, a White House aide who served as Trump's speechwriter during the campaign.
Lewandowski, who served as Trump's first campaign manager until he was fired in June 2016, has remained close to the president and the West Wing, serving as an outside adviser to the businessman-turned-president since his election.
"Even if he didn't work in the White House, we need to know everything he knows about events that occurred during the administration, such as the Comey firing, the letter that was written to cover up the [Trump Tower] meeting and other events," Rep. Joaquin Castro, D-Texas, told ABC News.
Lewandowski was initially interviewed by the committee in January but refused to discuss his activities and communications with Trump after being fired from the campaign.
Schiff said Thursday that Lewandowksi did answer some questions about the time period after his departure from the campaign.
The committee, split along partisan lines during its Russia investigation, has struggled to secure testimony from several Trump associates and confidants.
Lewandowski's refusal to testify came just days after former White House chief strategist Steve Bannon refused to discuss his work for Trump during the transition and in the West Wing, a move that prompted the committee to subpoena him on the spot.
Bannon returned to speak with congressional investigators in February, but told lawmakers he was instructed to invoke executive privilege on Trump's behalf. Republicans and Democrats are divided over whether to hold him in contempt of Congress.
Outgoing White House communications director Hope Hicks appeared before the committee last week, and did not answer some questions about the Trump administration and her time in the West Wing.
Republicans on the committee have increasingly signaled that they see their Russia investigation coming to a close, and hope to release findings and security recommendations ahead of the 2018 midterm elections.
"We're closer to the end than the beginning," Rep. Mike Conaway, R-Texas, a member of the House Intelligence Committee who is leading the probe, said Wednesday.
Stewart accused Democrats of working to prolong the investigation indefinitely, and claimed they recently proposed a list of roughly 100 additional witnesses they hope to interview.
"Some of them are Russians, one has actually passed away. There's a whole series of reasons of why we aren't going to be able to talk to these people," he said.
Democrats, who disputed Stewart's characterization of the list of additional witnesses, argue that they need to answer unresolved questions in their investigation and track down additional leads.
"The tragedy of the investigation is that there are so many leads that we could follow that are not being followed at all, so many trails that are being ignored," Castro said, adding that the committee also needs to obtain documents and information to verify past testimony.
Recently, House Democrats have expressed a desire to interview former Trump aide Sam Nunberg about his time with Trump, after he announced he wouldn't cooperate with special counsel Robert Mueller and claimed that Trump "may have done something during the election" in a flurry of cable news interviews this week.
They also wish to compel previous witnesses to return to Capitol Hill to testify, including Bannon, Donald Trump Jr. and Erik Prince - whose testimony about meetings in the Seychelles with Emirati officials and a Russian investor with ties to Russian President Vladimir Putin has been called into question by a series of new reports.
The New York Times first reported that George Nader, an advisor to the UAE, is cooperating with special counsel Robert Mueller and recently gave testimony to a grand jury. The paper reported that he attended Prince's meeting in the Seychelles with Kirill Dmitriev of the Russian Direct Investment Fund. Prince told lawmakers under oath that he met briefly with Dmitriev, and "talked for 30 minutes over a beer, and that was it."
"It would be my hope that we could have Mr. Nader, special counsel permitting, come before our committee at the appropriate time, and that we also have Erik Prince come back before the intelligence committee so that we can determine which account is accurate," Rep. Adam Schiff, D-California, the top Democrat on the committee, told reporters Thursday.