Trump held no public events over the weekend, and while the White House insisted he was aggressively working the phones, it didn't appear as though the President -- the man who has touted himself as the greatest deal-maker in world history -- was making much of a difference. (Senate Minority Leader Chuck Schumer said Monday that he had not spoken with Trump since their meeting on Friday afternoon; he also called Trump "glaringly absent" in the negotiations.)

"I just don't think it helps for him to be involved at all," Arizona Republican Sen. Jeff Flake said of Trump on Sunday night. "The White House really hasn't been involved from what I've seen."

There's a simple reason for Trump's lack of active involvement: He doesn't possess any sort of deep policy knowledge on this issue and he is uninterested in educating himself on the finer points of the policy debates at work in the shutdown in order to have any sort of real influence over the way forward.

When Trump has waded into this government funding/immigration fight, he's managed to muddy the waters rather than make them clearer. His 55-minute public conversation with Democratic and Republican lawmakers earlier this month suggested he was very much open not only to a deal on DACA but a broader agreement on comprehensive immigration reform. Forty-eight hours later, Trump was angrily condemning plans to continue to allow immigrants from "shithole countries" into the US.

Last Friday, when Senate Minority Leader Chuck Schumer left his meeting with Trump , he said he believed a deal to avoid a government shutdown was in the offing. Within hours, he had been informed there would be no deal.

What explains that lurching between deal and no deal? The obvious answer is that Trump doesn't have a strong policy background on any issue other than trade. As a result, he is hugely persuadable -- usually by the last person who he talks to. So, what looks like a deal one minute turns into no deal an hour later. And, because he lacks interest in the policy nuance, misunderstandings abound as he agrees to things without even knowing he is doing so. (Witness Trump's seeming acquiescence to a "clean" DACA vote in that public meeting; House Majority Leader Kevin McCarthy had to step in to make sure Trump didn't agree to something without even realizing he was doing it.)

Because of his unfamiliarity with details, Trump winds up being broadly superfluous to the intricate sort of negotiations that wind up closing the gaps between Republicans and Democrats -- or even between Republicans and Republicans -- on major issues.

Remember Trump's involvement in trying to win over wavering Republicans for his hoped-for repeal of the Affordable Care Act? Time and time again, GOP senators would emerge from meetings with Trump bewildered at his lack of a grasp about the specifics of any sort of deal. Trump's pitch to these lawmakers was of the 50,000-foot variety: Hey, we're all Republicans and Obamacare is bad, right? There was very little engagement with specific concerns about, say, Medicaid expansion dollars in their states.

It all makes some sense when you consider the role Trump played in his real estate ventures. He was never the guy negotiating the nitty-gritty details. He was the guy who came in the room at the end to close the deal by the sheer force of his personality.

That's clearly the role Trump saw for himself in the these shutdown negotiations. This, from Kevin Liptak's terrific Trump piece over the weekend , is telling (bolding is mine):

"In phone calls on Sunday, Trump encouraged Sen. John Cornyn and Rep. Kevin McCarthy, the No. 2 Republicans in the Senate and House, to reach an agreement with Democrats. But as he did at the end of last week, he stressed they should come to him with a deal instead of offering his own ideas for a way out, according to a person familiar with the calls."

The reason Trump didn't offer his ideas for a way out of the shutdown is that he didn't have ideas for a way out of the shutdown. That, to his mind, isn't really his job. He's the closer. He comes in, signs the paper, shows everyone the signed paper and hands out the pen he used to sign it to some lucky person. That's the job.

The problem for Trump is that senators and House members don't have the same reaction to him that many in the business world do. They are not awed by being in his presence and, therefore, willing to do whatever his people tell them to do. They have their own constituencies and their own interests that exist entirely apart from Trump's charisma. (This is especially true when Trump's approval ratings sit in the high 30s/very low 40s.)

Trump was a bystander in the government shutdown talks because he simply had very little to offer. His lack of policy knowledge -- and his unstinting belief he already knows everything he needs to know -- make him, the President of the United States, largely irrelevant to the re-opening of the federal government. Amazing.