House Judiciary Committee Chairman Rep. Jerrold Nadler, D-N.Y., warned Wednesday that investigations into President Trump's dealings with Ukraine may not end after the Senate's afternoon vote in the impeachment trial, and that he may issue a subpoena for former national security adviser John Bolton.

Bolton, who was said to have referred to dealings between the Trump administration and Ukraine as a "drug deal," received a request from House Democrats to testify during the impeachment inquiry. After the White House instructed him not to cooperate, however, House Democrats opted not to issue a subpoena and said the president's instruction -- based on an assertion of privilege -- was evidence that could be used to justify an obstruction of Congress charge.

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When asked if it was likely that his committee or others would subpoena Bolton, Nadler said, "Yeah," and indicated that House Speaker Nancy Pelosi has given approval.

Bolton had said he would testify if subpoenaed by the Senate during the impeachment trial, but the GOP majority decided that additional witnesses and documents were unnecessary. Bolton did not say anything about a House subpoena.

Nadler said he did not know when a Bolton subpoena may come, but he may hold off for the time being. His committee is presently awaiting a ruling in a case where they have been seeking to compel the testimony of former White House counsel Don McGahn over Trump's assertion of privilege. The D.C. Circuit Court of Appeals heard oral arguments in that case in early January, and a ruling could come as soon as Friday.

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Meanwhile, the impeachment trial is set to reach its conclusion when the Senate votes Wednesday afternoon in a decision expected to result in Trump's acquittal.