House Intelligence Committee Chairman Adam Schiff said former National Security Adviser John Bolton refused to submit a sworn affidavit on President Trump's dealings with Ukraine after the Senate rejected additional witnesses and documents.

In an interview with MSNBC on Wednesday after the Senate voted to acquit Mr. Trump of charges he abused his power and obstructed Congress, Schiff, a Democrat from California, said House Democrats approached Bolton's counsel after the unsuccessful vote in the Senate.

The House "asked if Mr. Bolton would be willing to submit an affidavit under oath describing what he observed in terms of the president's Ukraine misconduct, and he refused," Schiff said. " So for whatever reason, he apparently was willing to testify before the Senate but apart from that, seems intent on saving it for his book. He'll have to answer for that."

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Bolton said last month before the Senate impeachment trial kicked off that he would testify before the upper chamber if subpoenaed. Democrats had pushed for additional testimony during the proceedings, namely from Bolton, and their efforts were bolstered after details from Bolton's forthcoming book were leaked and reported by the New York Times.

Bolton reportedly wrote in an unpublished manuscript that Mr. Trump directly linked $400 million in military assistance to Ukraine to investigations into his Democratic political rivals, including former Vice President Joe Biden. That conduct was at the heart of the first article of impeachment against Mr. Trump, abuse of power.

But last week, the Senate rejected a motion to allow consideration of additional witnesses and documents in the impeachment proceedings, rebuffing Democrats' hopes of hearing from the president's former national security council.

House Judiciary Committee Chairman Jerry Nadler said the House will "likely" subpoena Bolton. But Schiff suggested it's not yet known whether they will seek to compel testimony from him.

"There's been absolutely no decision made about whether to subpoena John Bolton or not subpoena John Bolton," he told MSNBC. "What we had decided in discussing this with the speaker is we were going to try the case, we would conclude the trial, and we would consider what next steps we should take afterwards"

Schiff and Nadler, a Democrat from New York, both served as impeachment managers in the Senate trial, presenting the House's case for why they believe Mr. Trump was guilty for abuse of power and obstructing Congress in the course of the Democrats' investigation into his conduct with Ukraine.

Bolton's book, meanwhile, is supposed to be published March 17. The manuscript was submitted to the National Security Council for review in late December, but the White House warned Bolton last month it contained classified and top secret information that could not be published or disclosed.