The relevant matter may be under section 1505:
...Whoever corruptly, or by threats or force, or by any threatening letter or communication influences, obstructs, or impedes or endeavors to influence, obstruct, or impede the due and proper administration of the law under which any pending proceeding is being had before any department or agency of the United States, or the due and proper exercise of the power of inquiry under which any inquiry or investigation is being had by either House, or any committee of either House or any joint committee of the Congress—
Shall be fined under this title, imprisoned not more than 5 years or, if the offense involves international or domestic terrorism (as defined in section 2331), imprisoned not more than 8 years, or both.
trump is using Comey's firing as both threat and promise of force: anyone who keeps investigating his and his campaign's ties to Russia will lose their jobs.
Obstruction is a serious matter. Just ask Scooter Libby. Just ask Richard Nixon.
trump is openly admitting to it now. His recent interview with Lester Holt revealed he'd wanted to fire Comey for weeks, that he questioned Comey three times about the investigations into the possibility Russia hacked the 2016 election, and that "the Russia thing" was on his mind.
Jesus FUCKING Christ, Congress.
This is what you're defending every time you curl up into a ball, roll over, and play dead.