WASHINGTON — Tim Morrison, a hawkish senior national security aide and Trump loyalist in the White House, may be the best chance Republicans have for an impeachment witness who helps back up their defense of President Trump.
Mr. Morrison, a longtime arms control expert who worked in Republican congressional offices for more than a decade, moved to the White House last year to work with John R. Bolton, then the president’s equally hawkish national security adviser.
Now, Mr. Morrison is expected to testify on Tuesday afternoon that he heard nothing illegal as he listened in real time to a July 25 telephone call between Mr. Trump and Volodymyr Zelensky, the president of Ukraine.
That assessment and his fierce commitment to Mr. Trump and Mr. Bolton — he has been called Mr. Bolton without the mustache — have made him a priority witness for the president’s defenders as the impeachment inquiry moves into a second week of public hearings, and Republicans put him on a list of witnesses they requested.
Mr. Morrison, a political appointee at the White House, told lawmakers that Ukraine was not a big part of his arms control portfolio until July 2019, when he became the deputy assistant to the president for national security in charge of Russia policy. That was just weeks before the call between Mr. Trump and Mr. Zelensky that eventually prompted Democrats to officially begin the impeachment inquiry.
Democrats say that despite his loyalty to Mr. Trump, Mr. Morrison backs up their main argument for impeaching the president: that military assistance for Ukraine was held up to pressure the country’s leaders to announce investigations of the president’s political rivals.
In his closed-door testimony last month, Mr. Morrison described a call between the president and Gordon D. Sondland, a donor to Mr. Trump’s inauguration and the United States ambassador to the European Union, in which Mr. Trump insisted that Ukraine must publicly announce investigations into former Vice President Joseph R. Biden Jr. and his son and other Democrats.
Mr. Morrison has also testified that he and Mr. Bolton were deeply skeptical of efforts by Mr. Sondland and Rudolph W. Giuliani, the president’s personal lawyer, to conduct a shadow Ukraine foreign policy. In his testimony, he revealed a private meeting in which Mr. Bolton and others tried unsuccessfully to persuade Mr. Trump to release the aid to Ukraine.
But Republicans are likely to focus on the parts of Mr. Morrison’s testimony that support their arguments on behalf of the president.
Unlike some of his colleagues, Mr. Morrison has said he was “not concerned that anything illegal was discussed” on the July 25 call. (Jennifer Williams, a top national security aide to Vice President Mike Pence, said the call was more political than usual and was “unusual and inappropriate.”)
And Mr. Morrison also testified that the reconstructed transcript of the call was placed on a highly secure server by mistake, potentially undercutting the Democratic argument that the White House did so as part of a cover-up.
Representative Jim Jordan, an Ohio Republican who was temporarily added to the House Intelligence Committee so he could aggressively question the Democratic witnesses, tweeted over the weekend that Mr. Morrison would back up his party’s arguments.
Ronna McDaniel, the chairwoman of the Republican National Committee, retweeted Mr. Jordan and criticized Speaker Nancy Pelosi and Representative Adam B. Schiff, Democrat of California and the chairman of the Intelligence Committee.
“More testimony that vindicates @realDonaldTrump,” she wrote. “Pelosi and Schiff are grasping at straws.”
Mr. Morrison announced on the eve of his closed-door testimony that he would be leaving his position at the White House, though he insisted that his departure was unrelated to the Ukraine situation or his decision to testify.