First and foremost, is it correct to consider the process of impeachment and removal, in the US Constitution, a process of justice, but one administered in a political context? (That is, the opposite of a "recall election".)
If it is so, then how is a refusal to "send" an impeachment to the Senate not an act that obstructs justice?
The most relevant federal Obstruction of Justice type is from 18 USC 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—
I'm not sure if passed Articles of Impeachment count as an "inquiry", and I'm not sure whether failing to "send" them to the other house is "corruptly impeding". Even if those two conditions are met, members of Congress are immune to judicial process for acts taken while they are in session, as part of the Speech or Debate clause of the Constitution (Article 1, Section 6, Clause 1):
...shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their attendance at the Session of their Respective Houses, and in going to and from the same; and for any Speech or Debate in either House, they shall not be questioned in any other Place.
So, if the person in question is not a member of Congress acting in their official capacity and intentionally endeavors to prevent passed Articles of Impeachment from being sent from the House to the Senate (e.g. a courier intentionally failing to deliver them, or an IT person preventing the electronic form from being copied into the Senate's database), I do not know whether that could be considered Obstruction of Justice, as I doubt such a situation has ever been adjudicated. Given the publicity of the proceedings, such an impediment would probably be found out or overcome so quickly that no one would be inclined to do more than fire the perpetrator.
