WASHINGTON — President Trump’s first homeland security adviser said on Sunday that he was “deeply disturbed” by Mr. Trump’s effort to pressure a foreign leader to investigate his political rival, while Democrats moved forward with their rapidly evolving impeachment inquiry into the president.
The comments by Thomas P. Bossert, who served Mr. Trump as homeland security adviser from 2017 to 2018 until being forced out when John R. Bolton became national security adviser, amounted to a rare break with a president who prizes loyalty above all else. But Mr. Bossert tempered them, saying the central allegation against Mr. Trump — that he withheld military aid from Ukraine to advance his political interests — had not yet been proved.
“It is a bad day and a bad week for this president and for this country if he is asking for political dirt on an opponent,” he said on the ABC program “This Week.” “But it looks to me like the other matter that’s far from proven is whether he was doing anything to abuse his power and withhold aid in order to solicit such a thing.”
He also said another request Mr. Trump made to the Ukrainian president — that Ukraine investigate an American cybersecurity firm, CrowdStrike, and the location of a Democratic National Committee server — was based on a conspiracy theory that had been “completely debunked.”
That theory, prominent on the far right, holds that it was Ukraine, not Russia, that hacked into the server and intervened in the 2016 presidential election. But Mr. Bossert emphasized that American intelligence officials concluded that Russia was behind the hacking of the server, and he took the president’s personal lawyer, Rudolph W. Giuliani, to task for spreading the theory.
“At this point I am deeply frustrated with what he and the legal team is doing and repeating that debunked theory to the president,” Mr. Bossert said. “It sticks in his mind when he hears it over and over again.”
The comments came as the inquiry into the president rushed ahead at a dizzying pace. The Sunday talk shows — a staple of life in official Washington — were choked with lawmakers and other officials, even as Congress is on a two-week recess and most members are back in their home districts.
Representative Adam B. Schiff, the chairman of the House Intelligence Committee, said a whistle-blower whose complaint rocked Washington last week would testify “very soon.”
Mr. Schiff, a former prosecutor who is the de facto chief of the inquiry, also issued a pointed warning to Mr. Trump and the White House, who have a history of stonewalling Congress and refusing to turn over witnesses and records. “If they’re going to obstruct, then they are going to increase the likelihood that Congress may feel it necessary to move forward with an article of obstruction,” he said on “This Week.”
As Republicans struggled to defend the president on Sunday, Mr. Bossert’s remarks offered a hint of cracks in the Republicans’ armor. A handful of Republicans, including Senators Mitt Romney of Utah and Ben Sasse of Nebraska, have also said they were troubled by Mr. Trump’s effort to push the leader of Ukraine to investigate former Vice President Joseph R. Biden Jr.
And Representative Will Hurd, Republican of Texas and a former C.I.A. officer who is not seeking re-election, said Sunday that the allegations needed to be investigated. “There are troubling issues within the whistle-blower’s report,” he said on the CBS program “Face the Nation.” “But they are allegations. And I think that’s why we should explore these allegations through hearings. We’re — we had a hearing last week. We’re going to be having some depositions this week as well in order to get to the bottom of this.”
The inquiry centers on what amounts to a shadow foreign policy in Ukraine by the president and Mr. Giuliani. Central to the complaint by a whistle-blower was a July 25 telephone call between Mr. Trump and President Volodymyr Zelensky of Ukraine, at a time when the White House was withholding military aid to Ukraine.
A summary transcript of the call, released last week by the White House, shows that Mr. Trump asked Mr. Zelensky to “do me a favor” by investigating corruption in Ukraine.
Mr. Trump later brought Mr. Biden into the conversation, urging Mr. Zelensky to have a prosecutor look into Mr. Biden and his son Hunter, who sat on the board of a Ukrainian energy company when Mr. Biden was vice president. The younger Mr. Biden’s work has raised conflict of interest questions, but a former Ukrainian prosecutor said he found no evidence of wrongdoing by Mr. Biden or his son.
In his complaint, which the inspector general for the intelligence community deemed credible, the whistle-blower said the White House had tried to “lock down” all records of the call. Current and former White House officials have since confirmed that Mr. Trump used a secure system — intended for highly classified material — to store transcripts of that call and others with world leaders, even those that are not highly classified.
Democrats are accusing the White House of a cover-up, but Republicans have concentrated on another aspect of the call: Mr. Trump’s insistence that Ukraine investigate leaks about his 2016 campaign. Mr. Bossert called the situation “a mess,” and warned the president that if he did not end his fixation on what happened in 2016 election, it would “bring him down.”
Mr. Trump has long been suspicious of people in the federal bureaucracy — the so-called deep state — and the impeachment inquiry appears to be exacerbating the president’s fears that his own administration is conspiring against him. Stephen Miller, a senior adviser to the president, complained on Sunday of leakers who seek to destroy the president.
“If I don’t invite the right people the meeting will leak, if I don’t say the right thing they’ll go to the Hill,” Mr. Miller said, appearing on “Fox News Sunday.” “They’ve been doing this continuously for nearly three years.”
Republicans have had a tough time defending Mr. Trump, and have mostly been trying to redirect the conversation to insinuate that Mr. Biden engaged in wrongdoing. Representative Steve Scalise, the No. 2 Republican in the House, repeatedly changed the subject on Sunday when Chuck Todd, the moderator of NBC’s “Meet the Press,” pressed him on whether he believed a summary transcript of the Ukraine call merited further investigation.
“Well, they’ve been investigating President Trump for two years, making way for baseless allegations,” Mr. Scalise finally said. “They’re investigating everything.”
Senator Lindsey Graham, Republican of South Carolina, suggested that Mr. Trump appoint a special prosecutor to look into Mr. Biden’s role in the firing of a former prosecutor in Ukraine, and said he had no problem with the president’s call.
“I’m openly telling everybody in the country I have the president’s back because I think this is a setup,” he said on CBS’s “Face the Nation.”
Mr. Miller offered little concrete information on the president’s prepared defenses against impeachment, but the senior policy adviser did offer what could become the Trump administration’s narrative on Ukraine going forward: that the president is being martyred in a long war against government corruption by the deep state.
“The president is the whistle-blower here,” Mr. Miller said. “We have to focus on the real scandal, which is three years of deep state sabotage.”
Speaker Nancy Pelosi has said she wants the inquiry to move expeditiously, and her top lieutenants are following her lead. On Friday, three House committees issued subpoenas to Secretary of State Mike Pompeo, demanding that he produce a tranche of documents related to the Zelensky call.
This Friday, the Intelligence Committee will hold a closed briefing with the inspector general of the intelligence community, who conducted a preliminary investigation of the whistle-blower’s complaint and determined that it was credible.
“We have to flesh out all of the facts for the American people,” Mr. Schiff wrote Friday in a letter to his colleagues. “The seriousness of the matter and the danger to our country demands nothing less.”
Chris Cameron contributed reporting.