Washington (AFP) - Fired FBI director James Comey withheld judgment Thursday on whether President Donald Trump obstructed justice in requesting that he drop an investigation into his former national security advisor.
Instead he indicated before the Senate Intelligence Committee that it was up to a high-powered special prosecutor to determine whether the president's behavior constituted the potentially impeachable offense.
But what does the charge mean, and how might it lead to possible impeachment?
- The felony -
Obstruction of justice requires proof that a person has "corruptly influenced, impeded, or endeavored to influence or impede, the due administration of justice," says Ohio State University law professor Joshua Dressler.
It is not one crime but a family of overlapping federal crimes set out in statutes, says Brandon Garrett, professor law at the University of Virginia.
Someone does not necessarily have to try to end a pending, federal proceeding, only influence it, says Garrett.
- Establishing intent -
Intent -- defined as "corrupt" motive -- must be established and can be difficult to prove.
Acting improperly is not enough. The question is whether Trump crossed the line "fully aware that he was acting wrongly or whether he was oblivious to proper, established protocol," Dressler cautioned.
- Case against Trump -
Based on Comey's testimony, Dressler says you could make the legal case that all the elements of the crime of obstruction of justice is there.
But he said realistically it would take more to make impeachment suddenly more likely -- perhaps the existence of tapes that demonstrate collusion or support the idea that Trump tried to impede the investigation, or if someone else with first-hand knowledge comes forward.
It is also up for debate whether an FBI investigation even qualifies as a federal pending proceeding.
"The weight of the authority is that it is not... but a prosecutor could reasonably take a different view," Harvard University law professor Mark Tushnet told AFP.
It would be easier if a grand jury investigation had started and Trump knew that.
- Punishment -
In the courts, basic obstruction is punishable by not more than five years in jail, but a sitting US president has never been indicted and it remains an open question as to whether that is even possible.
It would also be near impossible to get a 12-person jury to reach a unanimous decision on such a case.
"Realistically no prosecutor, at least with what we've heard, would bring any action, just because you don't bring those kind of cases unless there is a slam dunk," Dressler said.
But obstruction was the basis of impeachment proceedings against president Richard Nixon in the 1973-74 Watergate scandal and Bill Clinton in 1998 over his affair with an intern.
- What is impeachment -
Impeachment is political recourse against a president at the hands of the House of Representatives with no legal indictment necessary.
Lawmakers only have to believe a president is guilty of "treason, bribery, or other high crimes and misdemeanors," to initiate articles of impeachment.
It is a two-step process.
A first vote takes place in the House, where a simple majority is needed.
In the event of impeachment, the case shifts to the Senate, where a two-thirds majority is needed for conviction in the 100-member chamber.
If that happens, the president is ousted -- with no recourse for appeal. Should the Senate fall short of conviction, the president is acquitted and remains in office.
No US president has been ousted from office under impeachment proceedings. Clinton was impeached by the House of Representatives in 1998 but acquitted in the US Senate. So was Andrew Johnson in 1868.
Richard Nixon resigned in 1974 to avoid impeachment.
- Not there yet -
Given that the House is currently controlled by the Republican Party, few experts believe Comey's testimony alone is enough to proceed against Trump.
The existence of tapes or the testimony of someone with first-hand knowledge could serve as catalysts, Dressler said.
"Then maybe the Republican Party would want to back away from Trump and actually initiate impeachment proceedings, but I don't think they're anywhere near willing," he said.
The climate could change should the Democratic Party win back control of the House in the 2018 mid-term elections.
But even senior Democrats say it is too early to call for impeachment, and that the facts of the case must first be established.