Democrats:
Please See: Executive Privilege.
It's not even that. That could be litigated in court, if this was a real subpoena. This is literally a fake subpoena. The House will never take the WH to court to get a court order, which is how these are enforced and litigated.
All the House will get is the right to call a contempt of Congress.
These are nonsense documents. "Pursuant to our legislative oversight power we command appearance for an impeachment investigation" is legal nonsense. A bad parallel would be "Pursuant to our power to oversee intelligence, submit your tax returns."
The difference is that impeachment investigation power belongs to the whole House, and the whole House has NOT delegated that power to any committee.