There will undoubtedly be a lot of content appearing in the next few months about congressional subpoenas and how to enforce them, along with the related topics of contempt of Congress and executive privilege. Most of this will be review for the regular readers of this blog (you can click on the “congressional investigations,” “contempt of Congress” or “executive privilege” categories to see Point of Order’s prior posts on these topics), but you still might want to check out this podcast featuring Molly Reynolds of Brookings and former House General Counsel Stan Brand, which provides a good overview of the subject as well as some history of the House Counsel’s office (you can find out, for example, why Neil Gorsuch might not be the biggest fan of the congressional subpoena power).
As Stan explains, the biggest problem with congressional subpoenas is that there is no clearly established mechanism to enforce them against the executive branch. Civil contempt is the only currently usable method, but it faces a number of obstacles, the greatest of which is that it is somewhere between extremely difficult and impossible to get a resolution within the time frame of a two-year congress. This gives the Justice Department and its clients a strong incentive to delay as much as possible, knowing that by the time a court gets around to deciding the dispute, it is likely that the whole matter will be moot.
As it happens, I have proposed a reform to House rules designed to address this problem (you can read about it here). Thus far the House in its wisdom has not seen fit to adopt this proposal, but perhaps someone will bring it to the attention of the new House Select Committee on the Modernization of Congress.