When US presidents talk tough to foreign leaders, does it work?

This question arises, of course, due to President Trump’s strong rhetoric this week about North Korea and its developing nuclear program. First Mr. Trump vowed to rain “fire and fury” on North Korea if it threatened the US.

Then he doubled down, saying that his original choice of words might have been too tepid. At 6:30 a.m. on Thursday, the president tweeted that if Pyongyang acts unwisely “military solutions are now fully in place, locked and loaded.”

Presumably Trump’s point here is to make North Korea’s leaders think twice about continuing work on miniaturized warheads and missiles capable of reaching the US mainland.

(He may also want to project an image of firmness to a domestic audience; according to some accounts, the “fire and fury” line was an offhand ad lib.) If so, he’s doing something lots of other US chief executives have done. Presidents have long used what experts call “statements of resolve” to clarify positions and draw red lines in international disputes.

Presidents make these demonstrations of public firmness to try and get adversaries to behave in a manner the US wants. In some instances, such as the Cuban missile crisis, declarations of White House resolve have indeed contributed to geopolitical solutions, according to political scientists who study this topic. It’s not always empty bluster.

But few past presidential threats have been as inflammatory as Trump’s. And history shows that foreign leaders weigh other factors, such as a president’s perceived credibility and domestic popularity, when judging White House resolve and their own best course of action. Unsurprisingly, they also take military balance into account.

In the current situation it’s also possible that North Korea's President Kim Jong-un hasn’t noted Trump’s words this week as much different from past US statements. After all, Pyongyang makes lots of flamboyant threats itself. The Hermit Kimdom may register “fire and fury” as typical rhetoric.

“For us this is incredibly novel and interesting and bizarre,” says Jonathan Mercer, a University of Washington political science professor. “We don’t know what it seems like to the North Koreans.”

How tough is tough?

Presidents talk tough in all manner of ways. The spectrum of rhetoric ranges from explicit threats of force – think President George H. W. Bush vowing that the Iraqi invasion of Kuwait would not stand – to more subtle statements that hint of force or other punitive action.

They do this in part because it plays well with their own supporters – and in part because it is one of their more effective tools. The US gets better outcomes in international disputes when the president makes more resolute statements, according to Roseanne McManus, an assistant professor at Baruch College, City University of New York, who studied the issue for her new book, “Statements of Resolve: Achieving Coercive Credibility in International Conflict.”

This is so because rival leaders recognize that resolute statements can box a president in, committing them to one course of action or another depending on what an adversary does. Their own credibility is at risk. So if a president presses ahead with firm rhetoric despite such risks, this can persuade adversaries of their resolve.

For instance, in 1961, John F. Kennedy made many public statements committing the US to keep troops in Berlin no matter what the Soviet Union tried to do to force them out. USSR leaders ultimately believed him, and backed off from their own threats of use of force.

The same thing happened in the Cuban missile crisis of 1962. Due to Kennedy’s public statements, as well as private negotiations and a naval blockade, “Soviet leaders became convinced that the Kennedy administration was resolved enough to attack Cuba and agreed to withdraw the missiles several days later to avoid war,” writes Dr. McManus in “Statements of Resolve.”

Not another Cuban missile crisis

The current situation is far different than those dramatic 13 days in October 1962.

For one thing, Trump’s threats are somewhat vague – is he threatening use of nuclear force, or not? What is his red line – more North Korean missile tests, or continued North Korean rhetoric, or what? In history, the more specific a US president’s threats, the better the outcome.

Trump’s statements are bellicose, and meant to be so. Or, as McManus puts it, his statements are “extremely resolved.”

“Trump is escalating things,” she says.

Plus, unlike JFK, the current president’s domestic support is suspect. He is feuding with a Senate majority leader of his own party. His approval ratings are very low. His White House staff has recently been in turmoil and his own cabinet has been contradicting him on certain aspects of his North Korean rhetoric. Secretary of State Rex Tillerson has appeared to try and reduce tensions, saying it was OK for Americans to “sleep well at night.”

All these things may make it less likely that Trump can follow through on his threats.

“In terms of his domestic standing, it is not very great. That might be his biggest limiting factor,” says McManus.

How North Korea sees it

There is also the question of how the North Koreans are interpreting Trump’s threats in the first place, much less whether they believe he can carry them out.

Generally speaking, most US adversaries spend a lot of time studying how the US government operates, what the president and other political leaders are saying, and how that affects possible US international actions. Consider Russia – its hacking of the 2016 presidential election reflected a sophisticated understanding of the trends and forces of US politics.

Is North Korea that sophisticated? Nobody knows. They are opaque, a riddle wrapped in a mystery and stuffed in an enigma.

Given that, we have no idea how seriously they take Trump’s threats.

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“It’s important to remember that credibility is in the eye of the beholder. It is not some objective property,” says Dr. Mercer of the University of Washington, who specializes in international security and political psychology.

Of course, it is not entirely clear what Trump’s threats are. And the fact that nuclear weapons are involved means that a miscalculation, however unlikely, risks terrible consequences.