Obstruction of justice is a criminal charge that, in general, can be laid whenever a person obstructs prosecutors or other officials in the course of investigating or prosecuting criminal activity. Its exact definition can vary under different state and federal laws, but the following are typical examples of grounds for obstruction of justice charges:
The question of whether Trump obstructed justice is governed by the definitions contained in Chapter 73 of Title 18 of the U.S. Code, specifically sections 1505 and 1512. Section 1505 makes it a crime to “endeavor to influence, obstruct, or impede” “any pending proceeding… before any department or agency of the United States.” Section 1512(c)(2) penalizes anyone who “otherwise obstructs, influences, or impedes any official proceeding, or attempts to do so.” It will be up to Special Counsel Robert Mueller to determine whether Trump fired Comey in order to impede the FBI investigation into Flynn’s ties to Russia. Even Trump’s request that Comey stop investigating Flynn arguably constitutes obstruction of justice under Section 1512(c)(2) as an improper attempt to influence or impede the FBI investigation.
A key aspect of an obstruction of justice case is whether the prosecutor can prove beyond a reasonable doubt that the person acted with an improper purpose. Many legal experts believe that Trump’s admissions about why he fired Comey are evidence of his improper purpose. As a sitting president, Trump cannot be indicted for the crime of obstruction of justice. But he could be impeached if the FBI findings are turned over to a congressional committee and the committee feels impeachment proceedings are justified.