Megan McArdle:

In my 20 years of writing right-leaning columns at mainstream publications, I’ve made two arguments over and over. First, I’ve tried to convince my fellow journalists that liberal media bias is real. And second, I’ve tried to convince conservatives that, though it’s real, it’s not the conspiracy they imagine.

This is a hard moment to make that latter point. Frankly, if we had been colluding to cover up the decline of a Democratic president, who then undid all our efforts by going on national television and breaking the story himself … well, how much different would our coverage have looked? And if he hadn’t self-immolated at the debate, wouldn’t our readers still be in the dark?

That said, it really wasn’t a conspiracy. For one thing, mainstream outlets did report on the president’s age, even if too gently. Why were we so gentle? Well, there’s a broad journalistic norm against picking on physical characteristics (which is why even certified Donald Trump-hating columnists have made remarkably few cracks about his comb-over)

Obviously, it was a mistake to treat age, which affects job performance, like hairstyling, which doesn’t. But that error was bipartisan — over the years, I’ve heard a lot of people talking about Trump’s senior moments without ever putting those thoughts on the page.

If Trump had slipped as visibly and publicly as President Biden, it’s possible we would have covered that more aggressively. But there was a paradox — the reporters watching him most closely were seeing tiny, incremental changes, without necessarily being struck, as were people who infrequently tuned in, with the cumulative magnitude of the decline. Also, Biden’s White House was simply more skilled at deflecting journalists who did notice: masters of killing stories with kindness and punishing reporters who wrote things they didn’t like.

I’m told that journalists who started asking about Biden’s age would suddenly be given access to normally unavailable senior staffers for denials, then deluged by allies insisting he was at the top of his game in private. It was genuinely hard to know how to balance those testimonials against reports of possibly isolated lapses.

“But the videos!” my conservative readers are sputtering, and fair enough — yet video clips can mislead unless you know the context. (Remember the Covington Catholic fiasco?) The White House made it hard to get that context; staff rarely leaked, and anyway, few people outside Biden’s inner circle saw him enough to form a complete picture of his condition. The inner circle, meanwhile, is dominated by people who have been with the president for years.

A few phenomenally dogged reporters persisted anyway. But they weren’t rewarded for it because there seemed to be no audience for coverage of Biden. Articles languished unread, and Biden books weren’t selling.

Not good enough, I can hear my conservative readers saying. Okay, the White House made it difficult to get the story — but if Trump were president, reporters would have been more skeptical of White House spin, more motivated to crack the wall of silence to meet audience demand. And all I can say to that is: Yeah, you’re right.

The media’s treatment of Biden wasn’t a conspiracy to protect a Democratic president, but it looks like one because that was its practical effect. None of our decisions were entirely driven by partisanship. But if we’re honest, many of them were unduly influenced by it.

Because there are 10 times as many Democrats as Republicans in mainstream newsrooms, journalists tended, with a few noble exceptions, to give a Democratic administration trust it didn’t deserve. The president’s invisibility was a giant red flag; they treated it as a restful break from having to monitor Trump’s ravings 24/7. As Biden’s decline grew more visible, people kept respectfully airing the administration’s insultingly implausible claims: that there was a secretly brilliant president flitting around the back corridors of the White House like Batman, while the videos of that same president acting befuddled on world stages were “cheap fakes.”

And when journalists did cover the issue, many outlets that had been pitilessly clear about Trump’s defects apparently couldn’t bring themselves to be quite so blunt about a president they liked — in part because that would make their friends mad, as well as the White House. A lot of articles about Biden’s age ended up so couched in ethereally vague language about “questions” and “concerns,” so defensively swaddled in equivocal context that the necessary SOS didn’t get through.

As a result, viewers of Fox News understood the president’s condition better than our audiences, which ought to be a huge wake-up call for us. We don’t have the exact problem conservatives imagine, but we do have a problem. And the only way to fix it is to add more viewpoint diversity to our newsrooms.

We should do this not for the benefit of conservative journalists, or politicians, but for the benefit of our readers. When our newsrooms lopsidedly support one party, our readers miss much of the story — in this case, nearly all of it. We need conservatives inside the building, helping us overcome our natural biases, instead of outside, complaining about them. We owe our readers, and our country, nothing less.