Update No. 2: For the fourth time in four days, Trump has pretty clearly responded to something he saw on the news by taking to Twitter. Here's Stelter, once again, with the eagle eye:

Update Thursday: Trump has now done it again, tweeting that Chelsea Manning is an "ungrateful traitor" 14 minutes after Fox News ran that phrase on its screen, as CNN's Brian Stelter notes. Trump also said it suggested Obama was a "weak leader," as Fox had.

The original post, from Wednesday morning, is below.

Over the past 12 or so hours, President Trump has made two major policy pronouncements via Twitter. On Tuesday night, he said he may “send the Feds!” to combat the “carnage” in Chicago, and on Wednesday morning, he said he planned to launch a “major investigation” of voter fraud.

Both of these things can pretty easily be traced back to one source: Trump's television.

As the Huffington Post's Michael Calderone noted late Tuesday night, Trump's tweet about Chicago came shortly after Fox News Channel's Bill O'Reilly ran a segment using the exact same statistics. Here's the graphic O'Reilly showed:

And here's Trump's tweet:

228. 42. 24 percent. All were in the graphic on O'Reilly's show, which is a Trump favorite.

Earlier Tuesday afternoon, the idea of a voter-fraud investigation was a major, contentious theme of White House press secretary Sean Spicer's daily briefing. Three journalists pressed Spicer on a very logical question: If Trump truly believed that 3 million to 5 million illegal votes were cast in the 2016 presidential race, why hadn't he called for an investigation of this seemingly major scandal?

Spicer: Trump believes millions of people voted illegally (Reuters)

As I wrote Tuesday, he's the president now, and he has professed severe concerns about election integrity and illegal immigrants. So his lack of a call for an investigation after more than two months of pushing this falsehood was conspicuous and suggested that he wasn't terribly serious about it.

Well, now he has called for one. Apparently in response to the heated back-and-forths at the televised briefing and the ensuing coverage of those exchanges, Trump tweeted Wednesday morning that he will indeed push for an investigation. The Washington Post's Robert Costa reports that an unnamed Trump aide insists that this has been discussed for a while, but Spicer sure seemed to be slow-rolling the possibility on Tuesday.

Update: It's been brought to my attention that NBC's "Today" show ran a fact-check segment featuring chief legal correspondent Ari Melber just minutes before Trump's tweets, in which Melber said the lack of an investigation was "an inconsistency that is very hard to square.” The segment ran starting at 7:07 a.m. Eastern time and featured a discussion of the lack of an investigation as the clock struck 7:10 a.m.; Trump tweeted about the investigation at 7:10.

So here we are again, in a situation in which Trump seems to be reacting in significant ways to what he sees on TV and in the media.

Last month, Trump tweeted about canceling Boeing's contract for the new Air Force One shortly after a Chicago Tribune article was posted that quoted Boeing chief executive Dennis Muilenberg making comments critical of increasing opposition to free trade — in other words, the position central to Trump's presidential bid. (Trump insisted that he hadn't seen the article.)

In November, Trump tweeted about how he'd like to punish flag-burners with loss of citizenship of jail time. About half an hour before, Fox News had aired a segment about students at a Massachusetts-based Hampshire College reportedly burning the flag in protest of Trump's election.

And that's to say nothing of his regular skewering of journalists and news media outlets whose stories and segments he hasn't approved of.

Trump himself has basically copped to this behavior. During the campaign, NBC's Chuck Todd asked him where he got his military advice, and his response was, “I watch the shows.” Hillary Clinton's campaign put it in an ad.

The difference now, though, is that he's in a position to actually make major policy decisions on it — such as opening a large investigation and sending federal resources to urban areas.

Trump has made many bold Twitter pronouncements that appear to have fallen by the wayside — statements about his political views and preferred policies that may reflect momentary whims that will never find their way into official White House action. (Trump hasn't even really talked about flag-burning and Air Force One since his tweets in November and December.) And given the sheer volume of these proclamations, his supporters and even the media will probably forget many of them were ever made.

But when something happens like it did Tuesday at the White House news briefing, and Trump responds with a promise for a “major investigation,” it's impossible to ignore the fact that he's now in the position to make that happen quickly — and to be held accountable if he doesn't.

We'll see if he actually follows through on either of the things he promised since Tuesday night or if they'll fade into Trump's news-making vortex. But if he does go forward with them, we'll know what set it in motion.