There's a reason Trump's threat to shut down the border sounds so familiar

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President Donald Trump’s threat to shut down the border feels really familiar.

On Friday he pledged he’s going to shut down the southern border as early as this week, calling it a “very good likelihood.” But we’ve been here before, and he hasn't followed through.

Trump threatened to close down the border on the seventh day of the partial government shutdown in December because he wanted $5.7 billion for a U.S.-Mexico border wall. He also threatened to close the border 25 days before that, that time to “STOP THE DRUGS!” And he said he’d close the border in November and October, too. He actually tweeted variations of such threats a total of seven times since October.

This time, though, his aides went on Sunday news programs to say he’s really serious about the move, considering it a punishment to Mexico for failing to stem the tide of migrants flooding over the border to seek their legal right to asylum in the U.S.

The threat followed an official with U.S. Customs and Border Protection saying the border was at a “breaking point,” and Department of Homeland Security Secretary Kirstjen Nielsen saying Thursday that her department is “increasingly unable” to deal with the flow of migrants at the border.

But while Trump has the authority to shut down the border over national security concerns, he’s almost certain to face immediate legal challenges, and he’d have to first justify his decision before a divided Congress. However, both President Nixon and President Reagan set a precedent for sealing off the border, with Nixon shutting down sections to slow drug trafficking and Reagan briefly closing the border when a DEA agent went missing. Trump might only shut down highly trafficked sections of the border, too.

"I’ll just close the border," Trump told reporters Friday. "When you close the border, also you will stop a lot of the drugs from coming in."

Trump’s chief of staff, Mick Mulvaney, told ABC’s “This Week” that it would take “something dramatic” to keep the president from his border-shuttering pledge this time around.

“We need border security, and we’re going to do the best we can with what we have,” Mulvaney said.

Kellyanne Conway, senior White House adviser, told “Fox News Sunday” that “you can take the president seriously” when it comes to this most recent threat.

But Trump shutting down the border would punish Americans, too — at least economically. Mexico is a major trading partner, particularly for the farmers that shuttle their crops across the border each day. And hundreds of thousands of people cross back and forth every day for business, school shopping and myriad activities.

“First, you’d see prices rise in­cred­ibly fast. Then . . . we would see layoffs within a day or two,” Lance Jungmeyer, president of the Fresh Produce Association of the Americas in Nogales, Arizona, told the Washington Post. “This is not going to help border security.”

The border shutdown would also follow the Trump administration’s dramatic move to cut off financial aid to El Salvador, Guatemala, and Honduras, over an unproven conspiracy that the governments of those three nations were provoking or “setting up” migrant caravans. Trump had threatened to cut off that cash flow previously, too, despite much of the aid already being appropriated in previous congressional spending bills.