If this Trump-vs.-Google thing blows up into something more than just another presidential rant — and it might, considering that the White House is “taking a look” at it and that Google on Tuesday joined Facebook and Twitter in receiving an Oval Office warning to “be careful” — then one day we can perhaps reminisce about how this chart started it all:

The illustration from Sharyl Attkisson, which appears to be a simplified version of Vanessa Otero’s viral bias chart, was a focal point in a post by PJ Media that apparently inspired this Trump tweet alleging that Google GOOG, +1.16% GOOGL, +1.13% manipulates its search to highlight liberal sites:

Trump didn’t cite any evidence in his tweet, but he did mention that 96% statistic.

He might have gotten the heads-up from Fox Business pundit and staunch Trump backer Lou Dobbs, who talked about it on his show Monday and also tweeted a link to the story:

Or, as Drudge claims, maybe it was this tweet:

This is nothing new, of course. Google parent Alphabet, along with Facebook FB, +2.12% and Twitter TWTR, +1.62% , are frequent targets of attacks for alleged suppression of conservative voices. Trump tweeted about it a few days ago:

Google says it’s not the case. Here’s the company’s statement:

“When users type queries into the Google Search bar, our goal is to make sure they receive the most relevant answers in a matter of seconds. Search is not used to set a political agenda and we don’t bias our results toward any political ideology. Every year, we issue hundreds of improvements to our algorithms to ensure they surface high-quality content in response to users’ queries. We continually work to improve Google Search and we never rank search results to manipulate political sentiment.”

Twitter’s Jack Dorsey also recently denied any such manipulation.

“We need to constantly show that we are not adding our own bias, which I fully admit is … more left-leaning,” he told CNN in an interview. “But the real question behind the question is, are we doing something according to political ideology or viewpoints? And we are not. Period.”

Dorsey and other tech executives are slated to appear on Capitol Hill next week to discuss, among other things, “algorithms and content judgment calls.”