– The House impeachment inquiry broke into a full-throated battle between the executive and legislative branches Tuesday, as congressional Democrats and Secretary of State Mike Pompeo traded threats and accusations, President Donald Trump questioned whether a leader of the probe should be arrested, and another senior Democrat said Trump should be imprisoned in "solitary confinement."

As the scope of the inquiry broadened, it touched a wide swath of top administration officials. In letters to Vice President Mike Pence and Energy Secretary Rick Perry, Sen. Robert Menendez, D-N.J., the ranking member of the Senate Foreign Relations Committee, demanded answers by Friday to questions about what they knew, when they knew it, and their roles in Trump's actions regarding Ukraine.

But much of the day's turmoil centered on Pompeo, who said in a letter to the chairmen of the House Foreign Affairs, Intelligence and Oversight committees heading the investigation that five State Department officials called to give depositions over the next two weeks would not appear as scheduled.

Pompeo characterized the effort to depose the officials as "an attempt to intimidate, bully, and treat improperly, the distinguished professionals of the Department of State."

By the end of the day, however, at least one of the five, former administration envoy to Ukraine Kurt Volker, planned to appear anyway before the committees Thursday. A second official, former U.S. Ambassador to Ukraine Marie Yovanovitch, would appear on Oct. 11, according to an official who spoke on the condition of anonymity.

Meanwhile, the committees were notified that the State Department's inspector general has requested to speak with them on Wednesday "to discuss and provide staff with copies of documents related to the State Department and Ukraine," according to a letter obtained by the Washington Post.

State Department Inspector General Steve Linick, whose office is responsible for investigating abuse and mismanagement in the department and operates largely independently from its control, "obtained the documents from the acting legal advisor of the Department of State," the letter said.

The inspector general does not have to seek Pompeo's approval to approach lawmakers with information, especially if the material is not classified.

It is unclear exactly what Linick will provide the committees. But the demand for any credible information related to Ukraine and the State Department is at a fever pitch as Democrats seek to build the case for Trump's ouster out of his newly revealed dealings with the government of Ukraine.

The inquiry centers on a whistleblower complaint, made public last week, alleging that Trump manipulated U.S. foreign policy for political gain, withholding aid to Ukraine while pressing its government to investigate the activities of Democratic presidential challenger Joe Biden and his son. That charge appeared to be borne out in a rough transcript of the call released by the White House.

Trump, who had put a hold on nearly $400 million in U.S. military assistance to aid Ukraine in resisting Russian incursions in its territory, urged President Volodymyr Zelensky to work with Rudy Giuliani, his personal attorney, and Attorney General William Barr in investigating Biden. He has charged that the former vice president intervened to squelch a corruption investigation of a Ukrainian company that employed his son, although Ukrainian officials have said Hunter Biden was not implicated in the investigation, which was later abandoned.

The committee chairmen responded to Pompeo with their own broadside, saying any attempt to prevent department officials from speaking to them "is illegal and will constitute evidence of obstruction," according to a statement issued by Rep. Eliot Engel, D-N.Y., who heads the foreign affairs panel.

Pompeo has publicly brushed off questions about the whistleblower's account, has been frustrated by Giuliani's efforts to implicate the State Department in his activities and insisted that it did nothing improper. Giuliani has said repeatedly that the department assisted his interactions with Ukrainian officials in pursuit of incriminating information on Biden, and a separate, but widely debunked, allegation that foreign interference in the 2016 election had come from Ukraine, rather than Russia.

"I have 40 texts from State Department officials asking me to do what I did," Giuliani said last week. "The entire idea that I did this on my own is total and complete bulls —."

"The whistleblower says the State Department was concerned about my activities," he said. "They shouldn't have been. They knew what I was doing."

Pompeo, in addition to expressing concern to some in the White House over Giuliani's frequent interviews and TV appearances on Trump's behalf, had argued against release of the Zelensky transcript, as did Treasury Secretary Steven Mnuchin, according to a senior administration official who spoke on the condition of anonymity.

Trump, however, appreciates Giuliani's tenacity and outspokenness, said a former senior official. "Trump doesn't differentiate between who is in the government and who isn't," the former official said.

On Friday, the committees also subpoenaed Pompeo over what they said was his failure to respond to previous requests to produce documents related to the inquiry. Pompeo left the country late Monday on a weeklong trip to Europe.

In a morning Twitter barrage, Trump repeated his insistence, despite information in the White House rough transcript, that almost everything the whistleblower said about it was "wrong," and asked, "Why aren't we entitled to interview & learn everything about the Whistleblower, and also the person who gave all the false information to him?"

Rep. Adam Schiff, D-Calif., chairman of the House Intelligence Committee, who broadly paraphrased the call during a hearing last week, had "made up" a version of the exchange, Trump said. He questioned why Schiff wasn't being "brought up on charges."

Later in the day, others entered the fray. Rep. Maxine Waters, D-Calif., who chairs the House Financial Services Committee, said the impeachment inquiry could expand beyond Ukraine. Impeachment, she said, "is not good enough for Trump. He needs to be imprisoned and placed in solitary confinement."

Republican National Committee Chairwoman Ronna McDaniel accused House Democrats of attempting "a legislative coup d'état" to get rid of Trump.