Democrats prove they're deadly serious about impeachment in warning shot to Mike Pompeo

House Democrats are moving with speed and certainty as they barrel forward with an impeachment inquiry of President Donald Trump.

In a new letter to Secretary of State Mike Pompeo, the Democratic chairs of three committees focused on Trump's pressuring of Ukraine announced that they are issuing a subpoena for documents related to the scandal. And they mean it, demanding his reply by Oct. 4, within a week.

The letter also includes a clear shot across the bow, signaling they're prepared to take this fight seriously: "Your failure or refusal to comply with the subpoena shall constitute evidence of obstruction of the House's impeachment inquiry." It noted that Pompeo has failed to comply with previous requests for documents earlier in the month.

"Your actions are all the more troubling given that since our September 9 request, it has become clear that multiple State Department officials have direct knowledge of the subject matters of the House's impeachment inquiry," it said. In particular, it noted that Rudy Giuliani, the president's personal attorney, has revealed that he has communicated with the department as part of his effort to influence Ukraine on the president's behalf.

"Your continued refusal to provide the requested documents not only prevents out Committees from fully investigating these matters, but impairs Congress' ability to fulfill its Constitutional responsibilities to protect our national security and the integrity of our democracy," the letter concluded.

The letter was signed by House Committee on Foreign Affairs Chair Eliot Engel, House Intelligence Committee Chair Adam Schiff, and House Oversight Committee Chair Elijah Cummings.

Democrats have also set a scheduled a rapid set of depositions of key officials related to the scandal between Oct. 2 and 10:

UPDATE: This report initially incorrectly said Democrats have subpoenaed Pompeo's testimony. Instead, they have subpoenaed State Department documents from him.