If they have any instinct for self-preservation, Iran and Hamas should be monitoring President-Elect Donald Trump’s communications closely these days.

A couple of weeks ago, there was the Truth Social post promising “ALL HELL TO PAY” if Hamas didn’t release its hostages by Trump’s inauguration on Jan. 20.

“Those responsible,” Trump noted, “will be hit harder than anybody has been hit in the long and storied History of the United States of America.”

He followed up during a press conference Monday. When asked what he meant by his prior threat, Trump left it menacingly vague. “Well,” he said, referring to our adversaries, “they’re going to have to determine what that means, but it means it won’t be pleasant. It’s not going to be pleasant.”

What does that signify? Does Trump have something in particular in mind, or is he making it up as he goes along? Is he bluffing? Or is he deadly earnest?

No one has come up with a Trump Doctrine yet, but a candidate might be: Find out if I’m serious or not at your own risk.

The most basic thing to note about Trump’s threat, though, is that it is the first time an official of the U.S. government — or a soon-to-be government official — has sounded appropriately outraged and harsh about an ongoing crime perpetrated against our fellow citizens.

Trump’s “hell to pay” is a throwback to Andrew Jackson or Teddy Roosevelt, making it clear that we aren’t to be trifled with, and doing it in a clarion tone.

It’s been shocking how muted the Biden administration has been about the hostages. Whereas Trump is expressing a righteous indignation in thunderous terms, the Biden administration has spoken as compellingly as a deputy Secretary of State summarizing the notes of a three-hour-long committee meeting.

This kind of jawboning comes naturally to Trump, of course. His approach doesn’t represent any particular foreign-policy theory. It’s not realist, or neocon, or isolationist. It’s less Clausewitz’s “On War” or Thomas Schelling’s “The Strategy of Conflict,” than Trump’s “Art of the Deal.”

The famous British line is that the Battle of Waterloo was won on the playing fields of Eton; in the same sense, every successful Trump negotiation as president has been won on the playing fields of Manhattan real estate, where Trump first learned his distinctive mode of gaining leverage and psychological advantage.

His willingness to escalate and follow through means no threat can be completely discounted, while his sheer unpredictably adds to the difficulty of any foreign actor trying to calculate his next move.