WASHINGTON ― After two years of failing to get Mexico to pay for a border wall as he had promised, President Donald Trump forced a partial government shutdown at midnight Friday over his insistence that American taxpayers foot the bill instead.

The impulsive, not-really-thought-through move has become the norm in Trump’s presidency. Whether it results in anything close to the billions he had demanded for wall construction is unclear ― and may well be beside the point.

Also unclear is how long the shutdown will last. Trump’s allies in the House added $5.7 billion in wall construction money onto a spending bill that had already cleared the Senate. That additional money remains a non-starter in the Senate, where 60 votes are needed to pass controversial legislation and where there are only 51 Republicans.

Trump, meanwhile, has already begun blaming Democrats for forcing the shutdown, even though he himself caused it by changing his mind at the last minute and insisting that the short-term spending bill moving through Congress include an unspecified amount of money for his wall.

“It’s up to the Democrats. So it’s really the Democrat shutdown,” the president said Friday during an unrelated bill signing ceremony at the White House.

Just 10 days earlier, though, in that same Oval Office, Trump had bragged to Senate Minority Leader Chuck Schumer (D-N.Y.) and House Minority Leader Nancy Pelosi (D-Calif.) that he would be happy to take the responsibility for a shutdown.

“I’ll tell you what, I am proud to shut down the government for border security, Chuck,” Trump said. “I will be the one to shut it down. I’m not going to blame you for it.”

Win McNamee via Getty Images Argue about a border wall or play golf? That is the question.

Three-quarters of the federal government has already been funded through next September under spending bills that Trump signed previously. But a handful of major agencies received only temporary funding because of the president’s earlier insistence that Congress start building his border wall, which Democrats refused to go along with.

The last of those funding extensions expired at midnight Friday. Both Trump and his White House had signaled during the first part of the week that he would accept another extension, this time through Feb. 8. By that point, Pelosi will have been sworn in as the new speaker, since the Democratic Party picked up 40 House seats in the midterm elections.

Some Trump allies believe that he will have an easier time negotiating a longer-term deal with her, offering to agree to some Democratic priorities in return for his wall. Other observers think that he has always preferred to attack Democrats over the lack of a wall than to actually build one, so that a Pelosi speakership will wind up being useful to him politically.

All those calculations changed Thursday morning, though, following a night and a morning of harsh criticism from Fox News hosts and radio talk show host Rush Limbaugh. Trump announced that he would reject any short-term spending bill that did not offer more money for border security, although he did not specify an amount.

Building a wall along the southern border and forcing Mexico to pay for it was Trump’s singular campaign promise, uttered for the first time in his Trump Tower speech announcing his candidacy. He repeated it hundreds of times between June 2015 and Nov. 8, 2016, when he won the presidency.

The “forcing Mexico to pay” part, though, was quietly dropped almost immediately upon his taking office. In a phone call with Enrique Peña Nieto, Mexico’s president at the time, Trump said that he understood Mexico would not pay for the wall but asked Peña Nieto not to say that publicly so Trump would not lose standing among his base.

In recent months, Trump has been conflating the “great, great wall” made of reinforced concrete that he promised during his campaign with a “bollard fence” design of steel posts that was adopted and started during President Barack Obama’s administration.

Of late, he has suggested describing his wall as “artistically designed steel slats” so Democrats won’t object to it as vociferously.

The shutdown will have little effect through the weekend and even on Monday, Christmas Eve, and Tuesday, Christmas Day, which are both federal holidays. But non-essential employees at the affected departments will be furloughed starting Wednesday, while employees considered essential ― including Trump’s Secret Service detail and many tens of thousands of workers in the Border Patrol, Immigration and Customs Enforcement, and the Coast Guard ― will be required to work without pay until the shutdown ends.

Trump postponed the start of what was to have been a 16-day golfing vacation at his private resort in Palm Beach, Florida, on Friday and remained in Washington instead. It is unclear whether he will stay at the White House until he signs a new spending bill or fly down to Mar-a-Lago in the coming days regardless.