It never should have taken a photo of Colbie Holderness’s bruised eye to get Rob Porter out of the White House.

He shouldn’t have been there as a top aide to President Donald Trump to begin with, given the longstanding and credible charges of domestic abuse from Holderness, along with another of his ex-wives and his former girlfriend.

It’s outrageous, but that’s what it took.

Porter’s resignation, which came on the very same day a photo of his ex-wife’s beaten face was made public by the Intercept, speaks volumes about how reality can prevail.

“Truth will out,” wrote Shakespeare in The Merchant of Venice.

Well, that was more than 400 years ago. Can we still count on that in an era of bot-powered hashtags and hyperpartisan lies?

“Conventional media is not equipped to deal with wilful lying in the public sphere,” wrote journalist Josh Marshall last week. Although he was talking about the infamous memo from House Intelligence Committee chairman, Republican Devin Nunes, his apt observation applies more broadly.

But in Porter’s departure, the truth came out, and action, long overdue action, followed.

Yes, there was lying, stonewalling and much talk at the highest levels about this man’s “true integrity and honour”. But go he did.

What made the difference?

It was the irrefutable proof that shut down all the bad-faith arguments against credible charges from credible people (“who can really know?”) and the stand-by-our-bro defences.

Such proof can come in many forms.

In the case of Alabama’s Roy Moore and his failed run for the US Senate, it came from a named, on-the-record, unimpeachable source, the brave woman named Leigh Corfman, who reluctantly agreed to tell The Washington Post how Moore initiated a sexual encounter with her when she was 14. Moore never recovered. The truth will out.

To be sure, even this kind of undeniable evidence doesn’t always carry the day. The Access Hollywood tape, in which Trump could be heard bragging about groping women, didn’t derail his presidential bid, but it did slow the train for a time.

In the days ahead, we’ll need more bulletproof, evidence-based journalism. And that’s not all we’ll need. Two other necessities stand out as the reality-based press grapples with growing challenges.

One is a greater willingness to forcefully call out the way political and civic norms are being turned upside down.

Just after Porter’s resignation last week, CNN’s Jake Tapper said on air: “I just wanted to once again note a further erosion of standards for what I thought we had all agreed was not OK, not acceptable, not moral. White supremacist rallies, child molesters, domestic abusers.”

Letting loose in a Meet the Press Daily monologue on NBC about covering the Trump Administration, Chuck Todd said: “It’s like we’re living inside a parody.”

News articles can’t make those kinds of assertions, but they can accomplish similar ends in other ways. The New York Times did it when it laid out, in a front-page article, Trump’s abnormal relationship with the law enforcement apparatus, tellingly headlined “Trump’s Unparalleled War on a Pillar of Society: Law Enforcement.”

The Washington Post did it in a prominently displayed story on how Trump has opted out of reading the President’s Daily Brief, a document that describes the most pressing information from American intelligence agencies.

Along with assembling evidence and pointing out changing norms, there’s a third crucial task for the news media now: consistently explaining to audiences how disinformation is spreading via technology.

After Russian-influenced bots reportedly helped stir up partisan outrage over the Nunes memo, Jason Schwartz of Politico looked ahead to an explosion of similar hashtags “designed to stoke anger, particularly among supporters of President Donald Trump against ‘deep state’ forces”.

The Nunes memo provided a handy playbook, he wrote, for how to move a concept from the fringes of the internet to mainstream outlets.

“Part of our role as journalists is to report on the information ecosystem, not to have a deliberately naive posture” about how lies are metastasising online, said Ben Smith, editor in chief of BuzzFeed, which has multiple reporters on this new beat.

Smith told me he’s hopeful that truth, through good journalism, will prevail, but he’s also able to imagine a bleak dystopian future.

Much depends, he believes, on the decisions that must be made by Mark Zuckerberg and Sundar Pichai, chief executives of Facebook and Google, respectively.

They need to face the reality of having to make editorial decisions about what’s true and what’s false.

Will they decide with an eye to the public interest rather than one fixed only on the bottom line? It’s far from clear that they will, but it matters immensely.

So, let’s see. We have a president who attacks civic norms, lies with impunity and is not adequately held in check by Congress. We have a media system, tainted by the likes of Sean Hannity and Tucker Carlson at Fox News, that enables him. We have unfettered technology that spreads disinformation in insidious new ways.

It’s not a recipe for a functioning democracy.

Thankfully, and in part because of good journalism, reality still manages to break through the murk.

Sometimes, it takes a photograph of a woman’s bruised face to force the truth to be acknowledged.

That’s a terrible lesson. It’s a lesson worth remembering.

• Margaret Sullivan is The Washington Post’s media columnist. Previously, she was The New York Times’ public editor, and the chief editor of The Buffalo News, her home-town paper