That is as it should be, because Bannon’s spurning of the committee strikes at the heart of democratic governance in two distinct but related ways. The first has to do with the committee’s substantive remit: It is investigating an attempt by Trump’s supporters to overthrow the government by force. Naming insurgents and their instigators and facilitators is one way to try to prevent these individuals from holding positions of power in the future. The committee can also try to put forward proposals to make this sort of event less likely to occur, and less likely to succeed, in the future.

But the particulars of this investigation aside, refusing to comply with any lawful congressional subpoena must have serious consequences. Congressional investigations serve a number of important functions: They can uncover social problems and shape new laws to solve them; they can reveal and help to rectify abuses by other government actors — including, at the extreme, through impeachment; and they can serve as an important mechanism for communicating with and making arguments to the broader public, a function I’ve termed “congressional overspeech.” Each of these functions is essential.

As the great legal scholar and New Dealer James Landis put it in 1926, “To deny Congress power to acquaint itself with facts is equivalent to requiring it to prescribe remedies in darkness.”