WASHINGTON — The Trump administration fought on multiple fronts on Tuesday to resist the House’s growing impeachment inquiry, pushing back on demands for depositions of potential witnesses from a key committee as President Trump insisted he was entitled to interview the whistle-blower whose allegations touched off the investigation.
Secretary of State Mike Pompeo threw up the first potential roadblock when he told lawmakers in a letter Tuesday morning that a demand from three House committees for American diplomats to sit for depositions this week amounted to “an act of intimidation” and did not allow enough time for the State Department to properly respond.
Meanwhile Mr. Trump, in an angry round of Twitter posts, suggested that the Democrat now running the impeachment investigation, Representative Adam B. Schiff of California, who leads the Intelligence Committee, should be arrested.
Mr. Pompeo did not refuse outright to allow the State Department employees to answer House investigators’ questions about the actions of Mr. Trump and his private lawyer, Rudolph W. Giuliani. Those issues are at the heart of the whistle-blower’s complaint, which details attempts by the president to pressure Ukraine’s leaders to help smear one of his top Democratic challengers, former Vice President Joseph R. Biden Jr., using Mr. Giuliani as a point man in the effort. But the letter cast doubt on whether Democrats would be able to begin the depositions as planned on Wednesday, and raised the possibility they might instead have to first issue a subpoena demanding compliance.
The House chairmen running the inquiry did not immediately respond to Mr. Pompeo’s letter, but were said to be preparing additional requests and subpoenas for information related to the case.
At the White House, an indignant Mr. Trump kept his focus on the anonymous whistle-blower whose complaint prompted the House inquiry. In a series of tweets, the president asked why he was not “entitled to interview” the person. The online venting came a day after Mr. Trump said the White House was trying to find out the person’s identity, despite institutional directives and confidentiality protections.
In addition to interviewing the “so-called ‘Whistleblower,’” Mr. Trump said on Tuesday, he would also like to interview “the person who gave all of the false information to him.”
The president’s remarks appeared to prompt a forceful, if not explicit, warning on Tuesday from a senior member of his own party. Senator Charles E. Grassley of Iowa, the senior-most Senate Republican and a longtime champion of whistle-blower laws, said the government and the media “should always work to respect whistle-blowers’ requests for confidentiality.” He did not explicitly mention Mr. Trump.
“No one should be making judgments or pronouncements without hearing from the whistle-blower first and carefully following up on the facts,” Mr. Grassley said in a written statement from Iowa, where he underwent surgery this week. “Uninformed speculation wielded by politicians or media commentators as a partisan weapon is counterproductive and doesn’t serve the country.”
Mr. Grassley also pushed back against a claim frequently repeated by Mr. Trump that the whistle-blower was a “fraud” because he was not a firsthand observer of the events he described in his complaint.
“Complaints based on secondhand information should not be rejected out of hand, but they do require additional leg work to get at the facts and evaluate the claim’s credibility,” Mr. Grassley said.
Mr. Trump’s latest attack on Mr. Schiff questioned why the congressman was not “being brought up on charges for fraudulently making up a statement and reading it to Congress.” The president was referencing remarks Mr. Schiff made during a hearing last week, where he dramatized the July phone call in which Mr. Trump pressed President Volodymyr Zelensky of Ukraine to work with Mr. Giuliani and William P. Barr, the attorney general, on investigations that would boost him politically.
Mr. Pompeo’s letter appeared more likely to have an immediate impact on the unfolding case.
In a letter and a pair of tweets sent from Rome, shortly after meeting President Sergio Mattarella of Italy, the secretary described the Sept. 27 demand for the senior State Department officials’ testimony as “an attempt to intimidate, bully and treat improperly” American diplomats.
“Let me be clear: I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead and serve alongside at the Department of State,” he wrote.
Standing with the Italian president, Mr. Pompeo ignored a question from journalists in Rome about his own participation in a July 25 telephone call between Mr. Trump and Mr. Zelensky of Ukraine that is at the heart of the impeachment inquiry.
House Democrats late last week subpoenaed Mr. Pompeo for documents and also asked for access to witnesses who were expected to speak to investigators this week. But given the recent disclosure that he also listened in on the telephone call, Mr. Pompeo himself could be subpoenaed to testify as well.
The State Department witnesses who have so far been called for depositions include Marie L. Yovanovitch, the former American ambassador to Ukraine who was recalled to Washington last May. Ms. Yovanovitch was instructed by the House to appear on Wednesday.
It appeared more likely that Kurt D. Volker, the United States special envoy to Ukraine, would appear for his scheduled deposition on Thursday. Mr. Volker resigned his State Department post on Friday, the same day the demand for his testimony was issued.
Other State Department employees who have been called are George P. Kent, a deputy assistant secretary of state for European and Eurasian affairs; T. Ulrich Brechbuhl, a State Department counselor; and Gordon Sondland, the ambassador to the European Union.
In his letter to Representative Eliot L. Engel, Democrat of New York and the House Foreign Affairs Committee chairman, Mr. Pompeo said the witnesses would not testify without Trump administration lawyers present. He also said the request did not leave the witnesses enough time to prepare for their interviews under oath.
But he did not rule out allowing the witnesses to talk to House investigators, and said the State Department would respond to the subpoena for the documents by the Oct. 4 deadline.
Mr. Engel and two other House Democrats who are chairing committees involved in the investigation sent two letters to Mr. Pompeo on Sept. 27. One said that the State Department had failed to comply with at least two earlier requests for information, starting Sept. 9.
The second letter warned Mr. Pompeo that a failure by the State Department employees to appear for their interviews “shall constitute evidence of obstruction of the House’s impeachment inquiry.” Mr. Pompeo replied that there was no legal basis for what he described as a “threat.”
“I urge you to exercise restraint in making such unfounded statements in the future,” Mr. Pompeo wrote on Tuesday.