Former national security adviser John Bolton "refused" to submit a sworn affidavit "describing what he observed in terms of the president's Ukraine misconduct" to House Democrats after the Senate voted not to hear witnesses in President Trump's impeachment trial, Rep. Adam Schiff (D-Calif.) told MSNBC on Wednesday.

Driving the news: Nadler said Wednesday it is "likely" House Democrats will subpoena Bolton and continue investigations into Trump's hold on military aid to Ukraine. Schiff told "The Rachel Maddow Show" that no decision had been made to subpoena Bolton.

What he's saying: ""For whatever reason, [Bolton] apparently was willing to testify before the Senate, but apart from that, seems intent on saving it for his book," Schiff told host Rachel Maddow. "He'll have to answer for that, but at this point we have not made a decision about whether or not to move forward with a subpoena, but it is certainly something that we will be discussing."

Flashback: Bolton said Monday that he would testify in Trump's impeachment trial should the Senate issue a subpoena.

The big picture: The Senate acquitted Trump of abuse of power and obstruction of Congress on Wednesday, with nearly every Republican declining to pursue new information about Trump's Ukraine activities.

Go deeper: Nadler says House Democrats will "likely" subpoena Bolton