The FBI probe into Trump and Russia is huge news. Our political system isn’t ready for it.

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: