Trump’s Jan. 6 subpoena is expected soon. But what happens next?

The House select committee investigating the attack on the U.S. Capitol on Jan. 6, 2021, is expected to issue a subpoena for testimony and documents from Donald Trump before the end of the week, wading into what could be a prolonged and unprecedented legal battle with the former president.

If Trump resists the subpoena, the committee faces a number of hurdles in compelling him to comply that could ultimately end in a constitutional showdown, according to legal experts and congressional counsel with experience in congressional oversight and investigations.

Trump has told...