President Obama must be ruing his famous dig at Mitt Romney — you know, “The 1980s are now calling to ask for their foreign policy back.”

Because Obama now faces overseas woes scarily reminiscent of the ’80s — and his defense secretary just said as much.

The zing came in the third presidential debate in 2012. “A few months ago,” Obama told Romney, “when you were asked what is the biggest geopolitical threat facing America, you said Russia, not al Qaeda.”

Then came the laugh-line about the ’80s asking for their foreign policy back — and the jibe, “The Cold War has been over for 20 years.”

Fast forward to last Tuesday, and Defense Secretary Ash Carter’s talk on the Pentagon budget at Washington’s Economics Club.

America faces five national-security threats, he said. Heading the list: the need “to deter Russian aggression” in Europe, which “we haven’t had to worry about . . . for 25 years.”

Oops. Back in 2012, Obama was promising Vladimir Putin he could be “more flexible” after he was re-elected. The years since have brought Putin’s response: Crimea annexed; Russian troops and proxies waging war on Ukraine’s government; Russian carpet-bombing of Syrian rebels, including US-allied ones, to prop up Bashar al-Assad’s bloody rule in Syria . . .

One of the two candidates clearly saw that coming — and it wasn’t Barack Obama.

So now Team Obama has belatedly caught up with Mitt Romney’s geopolitical foresight. Four years late.

A recent RAND study found that, should NATO try to answer a Russian military move in Estonia, Latvia and Lithuania, NATO forces would lose — in days.

But Ash Carter can’t even find the cash to restore the two combat brigades (of four total) that Obama pulled out of Europe in the wake of Hillary Clinton’s supposed “reset” with Russia.

US forces aren’t much better prepared to handle the next three blast-from-the-past threats on Carter’s list — China, Iran and North Korea.

Good news: When you get to the defense secretary’s No. 5 concern, you finally lose that vintage-’80s vibe. Bad news: It’s ISIS, which Carter warns is “metastasizing in Afghanistan, Africa and elsewhere.”

Obama once wrote off the Islamic State as a “JV team.” Even now, he’s leaving it to the next president to make good on his vow to “ultimately destroy” ISIS.

As Obama considers all these geopolitical threats and mulls his (self-limited) options, here’s a suggestion: Ask Mitt Romney for advice.