(CNN) Just 72 hours removed from signals being sent out of the White House that the President would sign a bill to keep the government open that did not include the $5 billion he wants for a border wall, Donald Trump reversed course Thursday -- telling Republican congressional leaders that he would not sign the short-term continuing resolution passed by the Republican-controlled Senate on Wednesday.

"The President informed us that he will not sign the bill that came up from the Senate last evening because of his legitimate concerns for border security," outgoing Speaker Paul Ryan told reporters after he and a handful of other GOP leaders huddled with Trump at the White House.

There was some inkling that Trump was moving in this direction. "When I begrudgingly signed the Omnibus Bill, I was promised the Wall and Border Security by leadership," Trump tweeted on Thursday morning. "Would be done by end of year (NOW). It didn't happen! We foolishly fight for Border Security for other countries - but not for our beloved U.S.A. Not good!"

But the finality of the announcement -- delivered by Ryan, not Trump -- throws Washington into total chaos. Consider: a) a good chunk of the government will shut down unless Congress finds a way to fund it (and Trump signs such a bill) before midnight Friday; b) it's not clear whether many of the House Republicans who lost reelection bids will come back to DC (and do so very quickly) if they are needed to pass some sort of border wall funding measure; and c) the math in the Senate to pass a major increase in the cash allocated for the border wall is hard to see, at best, and impossible at worst.

What led Trump to change his mind? To go from an annoyed willingness to keep the government open (and avoid being blamed for the shutdown) to a refusal to do so unless more money for his border wall made it into the legislation?

Here's my working theory:

Trump watches and is influenced by a LOT of cable television (we know this from his Twitter feed, in which he quote tweets supportive cable voices) Trump's go-to show is "Fox and Friends," the morning show on Fox News Channel -- his preferred cable TV network (we know this from his Twitter feed too) On Wednesday morning, the hosts of "Fox and Friends" blasted Trump's seeming capitulation on the border wall.

"What a stunning turn of events," said Steve Doocy. "If [Trump] agrees to the [short-term funding resolution] which would continue funding the government at the current levels ... he loses and the Democrats will win everything they want."

Added Ainsley Earhardt: "People who voted for him and want the wall and went to the polls to vote for that wall, they want to know how he's going to do this and they want to know why he seems to be softening his stance this morning."

If you think that criticism didn't impact Trump's thinking on the wall, you don't know Trump. He prizes his political base over all else. And he views "Fox and Friends" as the in-house programming for the base. If "Fox and Friends" is blasting him, Trump knows his base hears it. And he doesn't like to ever get sidewise with his base. (In that, Trump is not totally unique. Most politicians always keep an ear to what their base is thinking and saying. But no president has done that to the extent Trump has.)

Couple that critique with the parade of Freedom Caucus members who took to the House floor on Wednesday night to urge Trump not to sign the continuing resolution without his border wall money included and you see the roots of how Trump went from grumpy but willing to sign a short-term extension to keep the government open to adamantly opposed to doing so.

So where does Trump's latest switch leave us? Exactly nowhere. House Majority Whip Steve Scalise of Louisiana has indicated the House plans to try to add $5 billion in wall funding to the bill the Senate passed. It's not clear whether Republicans in the House even have the votes to make that happen. It's hard to see Republicans in the Senate gathering those votes with their very narrow 51-49 seat majority. If they had the votes to do that, Senate Majority Leader Mitch McConnell of Kentucky wouldn't have pushed to pass a small-bore spending extension -- without border wall funding -- on Wednesday night.

And that's before we even consider the fact that all of this has to happen, like, now. The legislative process, even when there is broad bipartisan support for a piece of legislation, moves slowly. There is no such agreement right now. And no real prospect that there will be any -- certainly not before 25% of the government is set to run out of money at midnight tomorrow.

The likeliest outcome -- by a lot -- right now is a government shutdown. Which will be applauded by Fox News and the Freedom Caucus, both of which will paint Trump's refusal to sign a short-term funding bill as a victory of principle over politics-as-usual. None of that will change the fact that we could start a new year with the federal government shuttered. Which is one hell of a symbol of the current state of our politics.