The House Judiciary Committee subpoenaed former Trump administration aide Rob Porter on Monday to testify in its probe regarding possible obstruction of justice by President Trump.

Why it matters: Porter was a key witness for the obstruction portion of former special counsel Robert Mueller's investigation. He resigned from the White House last year after his 2 ex-wives came forward with abuse allegations. Porter may never have to face the committee as the White House has moved to block other former surrogates from testifying before the House Judiciary.

Read the subpoena:

Go deeper: How Trump can stall House Democrats