Now that the first terror attack of Donald Trump’s presidency has taken place, we’re getting our first look at how the president is handling a serious domestic crisis in an area that was central to the whole story he told throughout the campaign — the tale about how relentlessly tough he would be on invading undocumented immigrants and terrorists.

The early returns are not encouraging. In response to the news that Sayfullo Saipov allegedly killed eight people and injured 11 in a truck rampage in lower Manhattan, Trump unleashed a volley of tweets that sniped pettily at Senate Minority Leader Charles E. Schumer (D-N.Y.) and demagogued about legal immigration. Still, I think there’s a hidden method behind his response that tells us something about where the immigration debate is heading next.

Here’s how Trump responded:

I have just ordered Homeland Security to step up our already Extreme Vetting Program. Being politically correct is fine, but not for this! The terrorist came into our country through what is called the “Diversity Visa Lottery Program,” a Chuck Schumer beauty. I want merit based. We are fighting hard for Merit Based immigration, no more Democrat Lottery Systems. We must get MUCH tougher (and smarter).

The “Diversity Visa Lottery Program” offers visas to people from areas of the world that have low immigration rates to the United States, and has been around for more than two decades. As The Post’s useful explainer details, it has long been a target of the right, and Trump and other conservatives want to end it as part of their current push to cut legal immigration.

Trump’s response is undercut by the basic history of this program. It’s true that Schumer did help create it, but the program was ultimately part of a broader bill that passed Congress by bipartisan votes and was signed by a Republican president. What’s more, as Sen. Jeff Flake (Ariz.), a Republican, quickly pointed out on Twitter, the comprehensive immigration reform bill the Senate debated in 2013 — which would have legalized millions of undocumented immigrants and boosted border security — actually ended this diversity program. That bill was, of course, blocked when House Republicans refused to act on it.

Based on the known facts, it’s also questionable for Trump to blame this attack on any failure of extreme vetting of arriving immigrants. Saipov arrived in 2010 from Uzbekistan — a country that is not on the list of those singled out for improved vetting by Trump’s thinly veiled Muslim ban. And New York Gov. Andrew M. Cuomo (D) told CNN this morning that he probably radicalized here, noting that current evidence suggests that “after he came to the United States, is when he started to become informed about ISIS and radical Islamic tactics.”

If this turns out to be right, then this story is more likely to be about why radicalization happens here than about the failure to keep out terrorists through tougher screening practices. But don’t take my word for it; listen instead to the Department of Homeland Security’s own analysts. As you may recall, a DHS memo was leaked earlier this year that concluded:

We assess that most foreign-born, US-based violent extremists likely radicalized several years after their entry to the United States, limiting the ability of screening and vetting officials to prevent their entry because of national security concerns.

Trump, of course, is trying to make this story about both the alleged need for stricter screening and the more generalized threat that legal immigrants supposedly pose. The argument doesn’t make much sense on its face: Does this one attack, as horrific as it is, really mean that reducing the flow of legal immigrants and orienting it more toward “merit” will make us meaningfully safer?

Regardless, it’s here that Trump’s demagoguing could directly affect the debate. The larger context here is that Republicans are searching for a way to make a deal that protects hundreds of thousands of “dreamers” from deportation, in exchange for increased border security and a “down payment” on the cuts to legal immigration that Trump and some conservatives in Congress want.

The problem is that even many in the GOP’s own ranks don’t want major cuts to legal immigration. Ending the diversity program, which would reduce legal immigration but not by large numbers, could be a way for Trump and conservatives to claim a “win” from a deal that ultimately protects the dreamers, giving the right something it has long coveted. The larger goal here would be to try to push Democrats off their current position, which is that they will agree to increased border security as part of any deal, but not to increased interior enforcement or cuts to legal immigration. Still, this is unlikely to work — Democrats probably won’t get knocked off this posture. But this is probably a key reason why Trump is trying to make the terror attack all about legal immigration so quickly.

* GOP’S SENATE HOPES EVAPORATING: National Journal reports that the GOP’s favorable Senate map is badly compromised by weak fundraising, the popularity of vulnerable incumbent Democrats and the terrible political environment:

The problems have grown so severe that it’s now as likely that Democrats will gain seats next year as it is that Republicans will expand their narrow 52-seat majority. … As things stand now, netting any seats would count as a victory. The emerging Democratic wave may not put Sen. Chuck Schumer in the majority leader’s chair, but it will drown out any hopes of passing conservative legislation of consequence beyond next year’s midterms.

Even if Dems can narrow the GOP majority by one seat or bring it down to 50-50, it would substantially complicate GOP chances of moving any big-ticket conservative agenda items.

Some conservatives … are urging Trump to consider another option that wouldn’t strike directly at the Mueller investigation — but might downplay the drumbeat of Russia news enough that the White House could return its focus to policy priorities. The idea: Setting up a competing special counsel probe that would examine an Obama-era deal that allowed a Russian-owned company to assume control of a slice of U.S. uranium extraction capacity.

It’s another sign that Trump’s allies are basically trying to create a vast alternate reality alongside the facts and charges emerging from the Mueller probe.

* BANNON PUSHES TO DEFUND MUELLER PROBE: The above Politico piece also reports that some Republicans are cool to Stephen K. Bannon’s effort to get Republicans to defund the Mueller investigation. But:

Bannon isn’t backing down. His next move, according to the person familiar with his thinking, is to try to build support for a proposal from Rep. Ron DeSantis (R-Fla.) that would end funding for Mueller’s office within six months of the bill being signed into law. … Bannon wants to … nudge House GOP leaders to get behind it — by making it a prime topic of discussion on conservative airwaves, including with Rush Limbaugh, Sean Hannity and Laura Ingraham.

You’ll be hearing a lot more along the lines of Hannity’s claim that Mueller, as FBI director, was complicit in the Uranium One scandal and that his probe has brought the United States to the brink of crisis.

* SOME REPUBLICANS WARN AGAINST MOVING ON MUELLER: The Post reports that some congressional Republicans are warning against targeting Mueller. Sen. Charles E. Grassley (R-Iowa) says Mueller is “very ethical” and “the process just ought to go.” And:

“There would be an uprising at the Capitol like never seen before if any kind of interference looked like it was taking place,” said Sen. Bob Corker (R-Tenn.). “Regardless of which side of the aisle. That’s just beyond the pale.”

This is good to see, but more like this would be even better.

* A BIG QUESTION ABOUT GEORGE PAPADOPOULOS: Rosalind S. Helderman has a deep dive into George Papadopoulos’s interest in Russia. This is a big, unanswered question:

Emails included in court documents released Monday show that Papadopoulos repeatedly told Trump campaign officials about his contacts with people he believed were representing the Russian government. The court documents do not answer a key question: whether Papadopoulos also told his superiors that he had met a London-based professor who claimed to know that the Russians had “dirt” on Democratic candidate Hillary Clinton, including thousands of her emails.

You can bet the country’s best investigative reporters are hard at work answering this question right at this moment.

* MAJORITIES WANT HIGHER TAXES ON RICH: A new CBS News poll finds that majorities want taxes hiked on corporations (56 percent) and on the wealthy (58 percent). And:

Most Americans are skeptical of the idea that corporate tax cuts would create jobs. About two-thirds of Republicans (63 percent) say corporations would use any money from potential tax cuts to create jobs, while most Americans (57 percent) overall disagree.

When Trump says slashing corporate taxes will cause growth to explode and corporations to hand over newly untaxed profit to workers, Republicans believe him, but most Americans don’t.

* AND ED GILLESPIE’S RACE-BAITING MAY BE WORKING: James Hohmann looks at a new Post poll of the Virginia gubernatorial race and finds the gap closing, with Republican Ed Gillespie’s Trumpist attacks winning over Trump voters without alienating independents:

If he prevails next week, it will be because he found a way to thread the needle in the age of Trump, maintaining his appeal to establishment Republicans while also wading into the fever swamps of Trumpism. … Top GOP operatives in the battle for control of the House tell me that they’re … running polls and using focus groups to gauge the potency of the wedge issues Gillespie has embraced — specifically MS-13 and “sanctuary cities.”

The polling averages have Democrat Ralph Northam up 3.6 points. Gillespie could very well win, and the stakes are high — if he does, 2018 will be a sewer.