Imagine someone had told you, a few years ago, that the FBI would soon be investigating a possible plot by a Republican presidential campaign to help Russia interfere in the US election — and that this interference had ultimately helped Donald J. Trump become president of the United States. You would have laughed in their face, or maybe accused them of confusing reality with a particularly lurid Tom Clancy novel.

But we learned on Monday morning that this is absolutely, 100 percent, without a doubt our reality. FBI Director James Comey confirmed it in testimony before the House Permanent Subcommittee on Intelligence, telling the assembled representatives that his counterintelligence investigators were looking into the Trump team’s links to Russia.

“[The FBI is] investigating the nature of any links between individuals associated with the Trump campaign and the Russian government and whether there was any coordination between the campaign and Russia’s efforts,” Comey said.

We’re so used to reports on Trump’s Russia ties that it’s easy to lose sight of the enormity here: There is an official FBI investigation into a presidential campaign’s possible collusion with a hostile foreign power for the first time in US history. Seasoned national security reporters, like the New York Times’s Matt Rosenberg, can scarcely believe it:

Folks, let’s take a step back and absorb the fact that the FBI has confirmed there is an espionage investigation involving the White House — Matthew Rosenberg (@AllMattNYT) March 20, 2017

Amid all the sturm und drang surrounding Trump’s fight with the press and intelligence community over leaks, all of the tweets, and hours of congressional hearings, this is what matters. We’re in the midst of what’s already a significant scandal — and one that could, depending on what the FBI uncovers, end up being the biggest political scandal ever in our history.

And it’s not clear, judging by the behavior of the Republicans at the House Intelligence hearing, if our hyperpolarized political system is capable of handling it.

The Russia investigation is absolutely huge

The mere fact of an FBI investigation isn’t proof that the Trump administration has actually done anything illegal. But the fact that there is an investigation at all shows the suspicions are at least serious enough to warrant a full investigation. And in this case, the FBI’s suspicions are supported by a lot of information that’s already in the public record.

We already know, for example, that members of Trump’s campaign, including former Trump campaign manager Paul Manafort, were in touch with Russian intelligence officers. We know that Attorney General Jeff Sessions, who also served as a foreign policy adviser to Trump during the campaign, met repeatedly with Russian Ambassador Sergey Kislyak before the election. We know that Russian intelligence hacked the emails of the Democratic National Committee and Clinton ally John Podesta. And we know that Trump confidant Roger Stone admits that he spoke to the Russian intelligence cutout who claimed responsibility for the DNC hack (who goes by the name Guccifer 2.0).

When you put this all together, there’s a clear and demonstrated pattern of contact between Trump’s closest associates and Russian officials. That is, in and of itself, disturbing: Political campaigns are not typically in the habit of communicating with countries that are currently bombing US military partners.

What’s more, there’s also a consistent pattern of Trump administration officials being less than forthcoming about their Russia ties. Former National Security Adviser Michael Flynn lied about his contacts with Kislyak, as did current Attorney General Sessions. The lies cost Flynn his job and forced Sessions to recuse himself from the FBI’s Russia investigation.

Yet Trump himself continues to deny, in the face of all this evidence, that there’s any story here:

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

This is why, even if nothing else is uncovered, the FBI investigation is so important. The president’s team has links to Russia that are objectively worrying — and has a routine pattern of lying and blaming the media when confronted with them. There’s a question of fundamental credibility, of why they feel the need to dissemble, at stake here.

The thought that the president may be lying, or at least not being fully forthcoming, about his administration’s ties to a hostile power is disturbing enough in its own right. The very fact that the FBI is investigating the administration two months into its tenure shows that things are not going well in the most powerful office in the world.

But if the worst-case scenario comes to pass, and the FBI finds hard evidence that the Trump campaign was in league with the Russians, then the already serious scandal becomes a national crisis.

“If [there’s] coordination, then this scandal becomes Watergate-like,” Michael McFaul, the former US ambassador to Russia, tweeted.

McFaul, if anything, understated the case. In Watergate, a presidential campaign authorized a break-in aimed at stealing sensitive information from the Democratic National Committee. This would be the exact same thing, only done digitally and with the help of a hostile foreign power.

It would represent collusion with Russian President Vladimir Putin to undermine American — and Western — democracy.

The notion that a US president could be involved in something like that should seem preposterous. The fact that the FBI is taking it seriously says volumes.

Our political system isn’t prepared for this kind of thing

If you want to understand how ill-prepared we are for a national debate over these allegations, look at Rep. Trey Gowdy’s performance during the hearing.

Gowdy was, in the past Congress, the chair of the House Select Committee on Benghazi, the ninth investigation into the 2012 attack on a US diplomatic mission in Libya. His committee spent two years and millions of dollars investigating allegations that the Obama administration or Hillary Clinton had personally covered up the truth about what happened in Benghazi — and, like all eight prior investigations, found no evidence to substantiate these claims.

So you’d expect Gowdy, advocate for truth and transparency that he is, to vigorously question Comey about Trump’s leaks to Russia. Instead, Gowdy spent a substantial amount of time naming former Obama administration officials — National Security Adviser Susan Rice, top aide Ben Rhodes, former Attorney General Loretta Lynch — and asking if they would have access to the identity of Trump associates whom the US intelligence community had identified as having spoken to Russians.

Essentially, he’s suggesting the Obama team illegally leaked classified information in an effort to gin up controversy about Trump.

“[By making] thinly veiled allegations against these former Obama administration officials by name … a member of Congress is intimating that particular Americans may have committed serious crimes,” a group of experts at the national security blog Lawfare write.

This is an allegation that you’ve seen, without any real substantiation, in some of the more unserious corners of the conservative press. Gowdy, by forcing Comey to admit that these people could have had access to relevant information, was seemingly intentionally fueling a conspiracy theory.

The Trump administration immediately jumped on this theory. Press secretary Sean Spicer highlighted it in his afternoon briefing to reporters.

“Director Comey told the House Intelligence Committee that certain political appointees in the Obama administration had access to the names of unmasked US citizens, such as senior White House officials, senior Department of Justice officials, and senior intelligence officials,” Spicer said. “Before President Obama left office, Michael Flynn was unmasked and then illegally his identity was leaked out to media.”

Gowdy’s line of questioning illustrates the way that most Republicans are handling this Russia probe: treating it not as an issue of major importance for the American public, but rather as an issue of loyalty to their president. The other Republicans on the House Intelligence Committee spent most of their time casting doubt on the idea that Russia would have wanted Trump to be president and lambasting leakers.

In a normal hearing, it would not be particularly troubling to hear Republicans playing defense for a Republican president. But this isn’t a normal hearing. This was convened to discuss what are, best case, demonstrated lies from the president’s team about its contact with a hostile power. Worst case, it’s an investigation into a political crisis without precedent in US history.

Yet in a political environment so defined by polarization, it’s hard for Republican legislators to think outside of partisan boxes. That’s how they approached the Benghazi investigation, when they were in the opposition and thus had an incentive to look for scandal; it’s how the party is approaching the Trump-Russia investigation now, when they’re in government and thus have an interest in turning a blind eye.

This is a very serious problem. The New York Times reports that FBI counterintelligence investigations can take years and don’t often lead to criminal charges. A congressional investigation in which Republican lawmakers subpoena Trump officials and force them to testify under oath would be a vital way of providing the public with information about these extremely serious allegations.

But Republicans, judging by Monday’s performance, seem to have no interest in providing this kind of oversight. Since they’re in the majority, they control whether or not there’s an official congressional investigation — and thus whether or not Trump officials will be forced to testify under oath. Partisanship may well be destroying our ability to get to the bottom of an issue of vital national concern.

Monday’s hearing was stunning in more ways than one.

Watch: Comey confirms FBI investigation