Then-FBI Director James B. Comey pauses as he testifies in March on Capitol Hill in Washington at a House Intelligence Committee hearing on allegations of Russian interference in the 2016 presidential election.  (J. Scott Applewhite/Associated Press)

The latest Post-ABC News poll finds: “A 56 percent majority of U.S. adults say [President] Trump is interfering with [investigations of possible Russian influence in the 2016 election] rather than cooperating, while 61 percent say Trump fired [FBI Director James B.] Comey to protect himself rather than for the good of the country.” Among Republicans, however, some 77 percent remain convinced, at least for now, that Trump is not interfering with the investigation. We will see whether testimony from Director of National Intelligence Daniel Coats today and Comey tomorrow shakes their confidence.

Comey has not endeared himself to the public; only 36 percent of Americans say they trust him a great deal or good amount on Russia and the election, while 55 percent trust him less or not at all. Compared with Trump, however, he’s a truth-teller — only 21 percent trust what Trump says, while an astounding 72 percent do not. Most surprising: “Trump’s trustworthiness also lags among fellow partisans, with less than half of Republicans (45 percent) saying they trust what he says about Russia investigations ‘a great deal’ or ‘a good amount,’ while about as many trust him less (48 percent).” This is one of the few concrete signs that he is losing support even among Republicans.

As we watch the testimony unfold, several considerations should be front and center.

First, Russia really isn’t the biggest problem for Trump; it is the replete evidence of obstruction that should keep him and his followers on edge. We have yet to see concrete evidence of secret collusion between the Trump camp and Russian officials (although it seems Trump publicly colluded by encouraging Russian hacking and using WikiLeaks’ hacked emails to support his argument that Hillary Clinton was unfit for office). There will be plenty of evidence on the obstruction front, however.

Second, obstruction does not require the underlying investigation to have merit. The issue for Trump, for Congress and for voters will be whether Trump was determined to get rid of Comey once he concluded that he could not control him (get him to take a “loyalty oath”). The selection of Christopher Wray, a Republican who defended New Jersey Gov. Chris Christie (R) in the Bridgegate scandal, may give Trump’s opponents the opening to say, “See, he wanted to get his own, partisan man in there.

Third, Trump’s defense — other than to squawk “Fake News! Fake News!” like a hyperactive parrot — may not center on “he said-he said.” With so many witnesses, it will be hard to dispute the words that came out of Trump’s mouth. One defense might be that he wasn’t trying to stop the investigation, but rather, to get rid of a “grandstander” whose credibility was under assault and who had politicized the FBI. The problem with that is that Trump reportedly asked Comey to lay off Michael Flynn, not just to adjust his public demeanor. He reportedly cleared the room when talking to Coats in an effort to enlist his help in shutting up Comey. In other words, he was perfectly willing to leave Comey in place — so long as he was “loyal,” meaning that he’d lay off the Russia investigation and Flynn in particular. Likewise, Trump’s fury at Attorney General Jeff Sessions’s recusal demonstrates that it was very important for him to leave the investigation under the oversight of his political cronies. In short, his problem with Comey and with Sessions’s recusal was his inability to affect the course of the Russia debate.

Fourth, we are curious whether any of the people who were asked to help stop the investigation had asked why Trump was so solicitous of Flynn. Did the president ever say why he wanted to spare Flynn? Considering that Trump has shown so little loyalty to so many people (Christie, a series of campaign managers, etc.), his devotion to this one aide strikes us as peculiar.

Finally, what’s going to be the GOP’s argument that all this does not amount to an impeachable offense? If Richard Nixon’s downfall was prompted by the discovery that he’d approved a plan to get the CIA to chase the FBI away from the Watergate break-in investigation, what’s the argument that a persistent pattern of trying to fire the head of the investigation and maintain his control of it through surrogates is not grounds for impeachment? Watching Republicans in Congress hem and haw, and twist themselves into pretzels trying to brush this all aside, should demonstrate once again how little they care about their oaths of office and fidelity to the Constitution and how much they have come to see themselves as Trump flunkies.