Rep. Elijah Cummings (D-MD), chair of the House Oversight and Reform Committee, would like the White House to provide documents. Any documents:
I have sent 12 letters to the White House on a half-dozen topics — some routine and some relating to our core national security interests. In response, the White House has refused to hand over any documents or produce any witnesses for interviews.
Let me underscore that point: The White House has not turned over a single piece of paper to our committee or made a single official available for testimony during the 116th Congress.
As a reminder of what used to be “normal,” previous presidential administrations turned over tens of thousands of pages of documents in response to Oversight Committee investigations under both parties just a few years ago. The George W. Bush White House gave us more than 20,000 pages relating to Hurricane Katrina; numerous documents and witnesses relating to the leak of covert CIA agent Valerie Plame’s identity; and nearly 1,500 pages of emails between senior White House officials about the death of Pat Tillman. Similarly, the Obama White House produced many documents and emails relating to the Solyndra controversy, as well as witnesses and documents regarding the Benghazi, Libya, attacks, including communication between top White House officials and National Security Council staff.
By contrast, the complete refusal by the Trump White House to produce any documents or witnesses to the primary investigative committee in the House reflects a decision at the highest levels to deny congressional oversight altogether. The president dictated this approach the day after the election when he threatened a “warlike posture” against Democrats and then vowed that, at the end of two years, “I’m just going to blame them.”
President Trump’s actions violate our Constitution’s fundamental principle of checks and balances. If our committee must resort to issuing subpoenas, there should be no doubt about why. This has nothing to do with presidential harassment and everything to do with unprecedented obstruction.
You don't want Congress to issue subpoenas if you're the president, because then you've lost control over what they'll see. My guess is that Rep. Cummings fired this shot across the White House's bow to let them know subpoenas are coming soon.