I’ve changed my mind about building a wall along the Mexican border. Build it!

The US government is shut down and the economic ramifications will be great. Not only are the families of people who’ve been put out of work being hurt, but the entire economy is going to be affected.

Challenger Gray & Christmas, a research firm, estimates that the shutdown could reduce consumer spending by $3.4 billion a month. And since the consumer is the biggest part of our economy, that’s going to smart.

The hard-headed politicians in Washington are clear: President Trump says there needs to be a deal on the wall before he’ll sign a budget. And the government can’t operate without that budget.

The Democrats say there will be no wall, so the positions seem to be fixed and the government remains shut. (More on that puzzling stance by the Democrats in a moment.)

But that’s not why I’ve changed my mind about the wall.

Let me first tell you quickly my long-held position on immigration. It’s simple: Immigrants are necessary. In fact, they are vitally important if the economy is going to continue to grow and if we want the budget deficit to go down and Social Security to be saved.

America’s population just isn’t growing fast enough to maintain a vibrant economy. Demographics are working against us — too many people are going into retirement age (when less is spent, less paid in taxes and more Social Security payments are handed out) and there aren’t enough people taking their places as workers and taxpayers.

So we need immigration. The more the better, in fact — except that we need people who will become employed and be the solutions to our problems and not add to the problems. We need workers, not freeloaders.

So why have I changed my mind about the wall? Because of the caravans of immigrants assaulting our southern border.

Building a wall just for a relative trickle of immigrants who’ve been crossing the border for decades would have been expensive overkill at a time when the US should have been watching its spending. There must be more cost-effective, high-tech ways to catch small groups of illegal intruders.

Now that “caravans” — the generally accepted word, not mine — are trying to enter the US from the south, the wall makes a whole lot more sense. In fact, Trump couldn’t have asked for a better excuse for his beloved barricade.

In the past there have been “caravans” of sorts coming into the US, only those were ships. The immigrants coming from Europe in droves came by floating caravans. But the difference was that they arrived here, were screened and allowed to stay if they were deemed not to become a burden on the social services system.

If people want to come from Latin America to the US, either by caravan or some other way, then they should undergo the same rigorous testing as those people in the ship caravans. They should come here legally!

Here’s the rest of what I think: Our politicians are acting like babies. Trump wants what he wants. And the Democrats have suddenly shifted their views on border security just to annoy the president and in hope that it gets him out of office in 2020.

Look at a June 24, 2013, article in the New York Times if you don’t believe me. The headline is “Senate Vote on Border Gives Push to Immigration Overhaul.” Barack Obama, a Democrat, was president at that time. Democrats controlled the Senate back then, Republicans the House.

Trump has said that all sorts of losers are trying to get into the country through Mexico. And there are probably some of those. Most of the people are fleeing persecution and are looking for a better life.

But the Democrats and the Republicans should be more concerned about another kind of threat. John Kelly, Trump’s former chief of staff, once said in an interview that the threat of terrorism from across the Mexican border “keeps me literally awake at night.”

“We know that would be the Super Bowl for the terrorists to knock down an airplane in flight,” Kelly said on “Face the Nation” on April 23, 2017.

The truth is that American intelligence agencies are afraid that terrorists have already snuck high-powered weapons across the Mexican border through tunnels. I have more details that I can’t share here.

Politicians on both sides of the wall are going to look very stupid if there is a big terrorist strike because of something that came through Mexico.