A FOG HAS DESCENDED on Washington, a kind of perpetual smoke screen created by President Trump that keeps his latest antics on the front page. By intent or accident, though, each day’s news also serves as a distraction. The lesson from Trump’s first 100 days is that it will take some discipline from the public to keep its eye on the ball: Russia.

The FBI and congressional investigations into Trump associates’ ties to Russia, and into the Russian intelligence service’s possible role putting him into the presidency, have no parallel in modern American history. Many questions remain unanswered, in particular what role, if any, the president played in the foreign meddling in our election. But the public must keep up the pressure for answers.

THE AVAILABLE FACTS suggest that Russian intelligence operatives helped Trump win the election against Hillary Clinton by hacking into her staff’s e-mail, leaking the damaging e-mails they found, and spreading false information through social media designed to harm her candidacy.

At around the same time, Russians had at least some communication with members of Trump’s campaign. Several of Trump’s current or former associates, including former campaign manager Paul Manafort and adviser Carter Page, have longstanding personal and financial ties to figures associated with Russian President Vladimir Putin. Russia also apparently targeted one of Trump’s Republican primary opponents, Florida Senator Marco Rubio.

None of the evidence made public so far proves anything, yet there’s too much smoke to ignore the possibility of fire. Here is the question that must be answered by a thorough, but expeditious, investigation: Did Trump himself know about, approve, or invite the Russian role in undermining our election?

For the House and Senate Republicans who control the intelligence committees, that should mean a refusal to play along with the White House’s repeated efforts to change the subject. In response to newspaper stories based on anonymous sources, for instance, the White House has sought to turn the focus on leakers, while ignoring the substance of the reports. The decision by House Intelligence Committee Chairman Devin Nunes to step down from the probe was a positive step, since Nunes appeared more interested in carrying water for the Trump administration than in conducting a credible investigation.

If Congress and the FBI are serious about getting to the bottom of the Russia issue, there’s no shortage of figures from the Trump campaign who might have useful information — and who might be induced to offer it up. For instance, retired general Michael Flynn, Trump’s former national security adviser, seems to have misled FBI investigators about his contacts with Russia and potentially violated rules barring retired military officers from receiving money from foreign governments.

The point of such an investigation, and of any probes into others involved in the president’s campaign, shouldn’t be to punish small fry for technical violations of the law. The point is to get the complete story about the president’s role, and get it soon. That’s true whether Flynn and others incriminate the president — or exonerate him.

WHILE CONGRESS and the FBI have an important job to do, the challenge for the rest of us may be even greater. The uncomfortable truth that the 2016 election exposed was that decades of poisonous politics have left the United States vulnerable to the sort of misinformation and manipulation that the Russian campaign allegedly ran, and to the flagrantly dishonest candidate that Trump was.

The Russians may have exploited our vulnerability in planting fake stories on social media, but Americans created it.

This is a country where a 28-year-old man in North Carolina believed the preposterous “Pizzagate” conspiracy theory enough to travel with an AR-15 to Washington to “self-investigate.” This is a country where Michael Moore’sconspiracy theories about the Carlyle Group and the Afghanistan war were indulged by Democrats in the 2000s. Kennedys and Trumps alike circulate misinformation about vaccines, and people believe them.

Paranoia is no longer just a style in American politics — to a shocking degree, it is American politics. Facts that don’t support neat ideological conclusions — even the idea of facts — have come under sustained attack. Donald Trump’s repeated lies barely registered with many of his supporters.

The Russians, it turns out, noticed.

If crimes were committed during the 2016 campaign, they must be punished, and investigators must follow the evidence as far up the chain of command as it goes. No matter how much distraction the White House and its allies churn up, Congress has to get to the bottom of Russian interference once and for all.

In a backhanded favor, Vladimir Putin’s government has already diagnosed America’s deeper problems.

Now it’s up to us to fix them.