Post Opinion columnists Ruth Marcus and Jennifer Rubin deconstruct the legal and moral quagmire President Trump faces following fired FBI director James B. Comey's testimony to the Senate Intelligence Committee on June 8. (Adriana Usero/The Washington Post)

Looking back years from now on Thursday’s testimony from former FBI director James B. Comey, we will likely see that it marked a turning point in President Trump’s drama. There was Before Comey and After Comey.

Before Comey, impeachment talk was not a real concern for Republicans. While they may still insist there is nothing to see here, Comey testimony’s turned impeachment into a serious topic of discussion. When you are debating whether an appalling course of conduct is illegal or “merely” impeachable, or whether it is as bad as the facts that led to Richard Nixon’s removal, the incumbent party is in deep trouble.

Before Comey, the 2018 elections might have been a referendum on the Trump agenda. After Comey, they surely will be a referendum on Trump, and specifically whether he should be impeached — unless, of course, Republicans decide to cut their losses and get rid of him before the midterms.

Before Comey, Republicans and Democrats had many bones to pick with Comey. After Comey, both sides avoid questioning his integrity. Republicans carped about his refusal to rebuke the president in the Oval Office (for a group that has never seriously confronted Trump on much of anything, this is rich). They made hay out of — gasp!– a leak of unclassified materials after Comey was fired. Not once, however, did any senator say he disbelieved Comey’s account or try to shake his recollection. Aspects of Comey’s factual account can be supported now by others, which will further bolster his own credibility and diminish Trump’s. Comey may be prickly, overly concerned with his own reputation and even a little schoolmarmish, but few will argue that he is a liar.

Before Comey, it was possible (although not likely) that Trump could have righted his ship, moving beyond the Russia scandal. After Comey, it is impossible to imagine that the “cloud” Trump so badly wanted to dissipate will vanish before the end of his term — which might well end before January 2021.

Before Comey, Republicans could argue that Trump had done nothing improper. They could say that he was in the clear, not involved in any criminal or counterintelligence investigation. After Comey, the best Republican members can say about him is that his conduct was “obviously” inappropriate. They cannot say with certainty that he is not under investigation for obstruction.

Before Comey, Republicans could argue that Trump understood the requirements of the job. After Comey, as Benjamin Wittes (a friend of Comey’s who spoke to him during the events at issue) put it, “There is no evidence that any chains can bind this president: not lawyers, not norms, not procedures, not repeated screw-ups of the sort that educate other leaders, and certainly not the mere expectations of decent public servants. But the problem is that the United States is responsible for his actions—and we are paying daily the price for them, particularly in our international relations but also in our domestic governance.” We have a legitimate question as to the president’s fitness for office.

Before Comey, it was possible for Republicans to defend the reputation and actions of the attorney general. After Comey, we know that investigators are looking at a possible third unreported contact between Jeff Sessions and the Russians. We also learned, according to Comey, that Sessions refused to interpose himself between the FBI director and the president when Trump cleared the room to talk to Comey alone, nor did Sessions respond when Comey told Sessions never to leave him alone with the president. (The Justice Department disputes this with a wooden statement: “The Attorney General was not silent; he responded to this comment by saying that the FBI and Department of Justice needed to be careful about following appropriate policies regarding contacts with the White House.” Even if one believes he said these words, there is no evidence that he spoke to the president.) As for the firing of Comey, we either must believe that Sessions was so dense he actually believed Comey was being fired for the handling of Hillary Clinton’s emails or that he was bludgeoned into reentering the realm of the Russian investigation — by arranging its lead investigator’s termination under false pretenses. Aside from Trump, no official has come off worse than Sessions in the past two days.

Before Comey, it was possible for national security adviser H.R. McMaster and other members of the administration (as well as GOP lawmakers) to argue that a secret back-channel with Russia was no big deal. After Comey, Americans understand that in setting up a channel to hide discussions from the intelligence community, you put American security at risk. Comey said, “You spare the Russians the cost and effort to break into our communications channels by using theirs. You make it a whole lot easier for them to capture all of your conversations. Then to use those to the benefit of Russia against the United States.” Comey, in other words, made clear that those seeking such an arrangement were just asking to be blackmailed by the Russians. (Other than Sessions, no one has sacrificed more credibility than administration officials such as McMaster who tried to rationalize such an arrangement.) This realization will prove very problematic to Jared Kushner and others trying to justify alleged involvement in such a scheme.

We may see other milestones and equally decisive moments before this is over. Certainly, any report or decision by the special counsel to file charges will dwarf what we have seen. For now, however, the course of the presidency, the nature of the Russia investigation and the ability of Republicans to defend a president who has been convincingly portrayed as a liar have dramatically shifted. There’s no unringing the alarm bells Comey sounded over the past two days.