That’s not how oversight has ever worked. Barr’s unilateral declaration—that any attempt by Congress to question him or his officials is illegitimate—is just the latest effort to place the executive branch above its constitutional obligations. The administration has spent recent years refusing to comply with congressional subpoenas for executive documents, most notably during the impeachment inquiry, but the refusal to even appear is a complete rejection and dismantling of oversight altogether. This latest effort calls for the only possible proportionate response: William Barr should be impeached.
Source: Impeach Bill Barr.