WASHINGTON — Trading hot charges of intimidation, the Trump administration took a defiant step toward resisting Congress’ access to impeachment witnesses Tuesday, then House Democrats warned such efforts themselves could amount to an impeachable offense.

In quick escalation, Secretary of State Mike Pompeo said the Democrats were trying to “intimidate” and “bully” five current and former career officials into testifying and providing documents. House investigators countered that it would be illegal for the secretary to try to protect Trump by preventing them from talking to Congress.

The exchange of accusations and warnings signaled yet another stiffening in the confrontation between the executive and legislative branches following the Democrats’ launching of the impeachment inquiry late last week. That followed a national security whistleblower’s disclosure of Trump’s July phone call seeking help from the new Ukrainian president in investigating Democratic rival Joe Biden and Biden’s son Hunter.

Some Trump supporters cheered Pompeo’s muscular response to the Democrats. But it also complicated the secretary’s own situation, coming the day after it was disclosed that he listened in during Trump’s phone call with Ukrainian leader Volodymyr Zelenskiy that helped trigger the impeachment inquiry.

“Any effort to intimidate witnesses or prevent them from talking with Congress_including State Department employees_is illegal and will constitute evidence of obstruction of the impeachment inquiry,” said three House chairmen, Adam Schiff of the Intelligence committee, Eliot Engel of Foreign Affairs, and Elijah Cummings of Oversight.