You might think that yesterday was just another Monday, just another beginning to a long work week.

You might be wrong. At least President Donald Trump's opponents hope that's the case.

Yesterday was indeed another beginning to a long work week, but it could prove to be more than that too. That's because FBI Director James Comey testified at a congressional hearing about the ongoing investigation into the Trump campaign's alleged ties to Russian officials who surreptitiously meddled in last year's U.S. election.

"After two months of Donald Trump's presidency and more than a year of his campaign, our political senses are so dulled by tumult that we can barely recognize history when we see it," veteran political reporter Howard Fineman wrote on Huffington Post. "Make no mistake. Monday's hearing was all but unprecedented."

The way the former chief political correspondent for Newsweek magazine interpreted the happenings on Capitol Hill: that not since the Watergate scandal more than 40 years ago "has an investigative hearing made it so clear that a presidency was in serious legal jeopardy."

Other news analysts reached similar conclusions: The Guardian, for example, reported that Comey's testimony "marked a remarkable and unprecedented threshold in U.S. political history, putting beyond doubt that a sitting's president's entourage was under investigation for possibly conniving with a foreign adversary to put that president in power."

Well ... we'll see if the FBI's investigation really does mean Trump is in trouble. It's far too soon to tell. That said, the president certainly responded to Comey's testimony as if his presidency is in serious legal jeopardy.

Comey, as usual, offered little in the way of specifics, insisting time and again: "I cannot say more about what we are doing and whose conduct we are examining." But his and National Security Agency Director Michael Rogers' testimony did provide meaningful public information. Here's what we know or appears likely, based on the hearing:

* Multiple people from the Trump campaign are being investigated.

* Former Trump campaign chairman Paul Manafort and Trump's former national-security adviser Michael Flynn might be under investigation for possibly violating the Foreign Agent Registration Act or for other reasons. (Flynn acknowledged last week that during the campaign last fall, while advising Trump on foreign-policy matters, he was working as a lobbyist for Turkish corporate and government interests. Manafort has long-standing lobbying ties with notoriously corrupt pro-Russian government actors in Ukraine.)

* The investigation into Trump campaign links to Russia started last summer, and Russia's interference in the election was "unusually loud" -- that is, so obvious as to be beyond any doubt in the U.S. intelligence community.

* Comey stated unequivocally that there is no evidence that backs up Trump's March 4 claim that former President Obama surveilled Trump or Trump Tower last year. "With respect to the president's tweets about alleged wiretapping directed at him by the prior administration," Comey said, "I have no information that supports those tweets. And we have looked carefully inside the FBI." Comey pointed out that the president doesn't have the ability or the authority to order such surveillance. Trump critics insist the president made the accusation simply to divert attention from the brewing Russia scandal.

* The claim that Britain's intelligence services helped Obama spy on Trump, an accusation advanced by White House press secretary Sean Spicer, is false. Rogers called the accusation "frustrating to a key ally." (NSA Deputy Director Rick Ledgett said in a recent interview that the claim is "nonsense ... just crazy.")

All of this was clearly damaging to Trump. Roll Call columnist Walter Shapiro insisted that Comey, the man Democrats have accused of sabotaging Hillary Clinton's presidential campaign and aiding Trump's last October, on Monday "gave an artful lesson in how to stick a shiv into a sitting president without ever raising his voice or making a specific accusation."

During and after the congressional hearing, Trump tried to change the subject from the substance of the press leaks that suggest untoward links between the Russian government and the Trump campaign (and led to the present investigation) to the leaks themselves. Trump and his White House also tweeted out misleading and confusing responses to Comey's testimony. Some examples:

FBI Director Comey refuses to deny he briefed President Obama on calls made by Michael Flynn to Russia. pic.twitter.com/cUZ5KgBSYP — President Trump (@POTUS) March 20, 2017

The real story that Congress, the FBI and all others should be looking into is the leaking of Classified information. Must find leaker now! — Donald J. Trump (@realDonaldTrump) March 20, 2017

The Democrats made up and pushed the Russian story as an excuse for running a terrible campaign. Big advantage in Electoral College & lost! — Donald J. Trump (@realDonaldTrump) March 20, 2017

Ezra Klein, who heads the news-analysis site Vox, cut to the heart of this tweet storm with a post on Facebook:

The lies don't get more clear cut than this: Posted by Ezra Klein on Monday, March 20, 2017

The Washington Post added its take on Trump's criticism of the media's reporting about the investigation: "Basically, the White House doesn't seem to understand the difference between a circumstantial case and a conspiracy theory."

The key questions that arise from Comey's and Rogers' testimony include: How long will the investigation take and how far afield will it go? ("This work is very complex and there is no way for me to give you a timetable as to when it will be done," Comey said.) Who specifically is being investigated beyond Manafort and Flynn, who are widely believed to be part of the probe? And, most important, what did Trump know and when did he know it?

Step by step, the FBI investigation and related congressional investigations will try to answer those questions. If the FBI has something on Flynn and/or Manafort, it likely will try to leverage that to get them to talk about the doings of other Trump campaign officials -- and specifically what Trump did or knew.

Comey, for his part, indicated he wants to get back to the business at hand, which for him is not testifying before Congress but pursuing the investigation.

"I'd rather not be talking about this at all," he said near the end of the hearing. "Now we're going to close our mouths and do our work."

-- Douglas Perry