In the House impeachment inquiry hearings, Gordon Sondland, David Holmes, Fiona Hill and other witnesses have relayed how President Trump appeared to withhold a White House visit with Ukrainian President Volodymyr Zelensky to pressure him to announce an investigation into one of Trump’s political opponents.

The nature of this particular concession may have been well outside the norm. But U.S. presidents frequently condition diplomatic visits on concessions from their foreign counterparts. William B. Taylor Jr., the acting U.S. ambassador to Ukraine, intimated as much in his testimony Nov. 13, when he compared diplomatic visits with other, less transactional instruments of foreign policy: “It’s one thing to try to leverage a meeting in the White House. It’s another thing, I thought, to leverage security assistance.”

As I show in recent research, co-authored with Alastair Smith, in-person diplomacy frequently serves as a medium of exchange in international dealings. And these encounters yield substantial benefits for recipient and granter alike.

There’s no such thing as a free visit

There is ample precedent for conditioning a White House visit on the delivery of a policy concession by the foreign government. For example, in a 1945 letter to the secretary of state, the U.S. ambassador to Paraguay reported informing his host government that “our attitude toward possible visits … would undoubtedly be influenced by the extent of the effort made” within the country toward democratization and the protection of civil liberties.

In 1955, a U.S. ambassador likewise advised postponing an invitation to Egyptian President Gamal Abdel Nasser to visit the White House. Such a meeting, the ambassador noted, would “accomplish much more if, prior to the visit, [the] pendulum in Egyptian-United States relations could by other means be started again toward United States.”

Leveraging official visits for policy concessions isn’t just a U.S. practice. For instance, the French and British governments of the 1970s were well aware that commercial agreements with Romanian President Nicolae Ceausescu could be smoothed out more quickly and favorably when they included a state visit to sweeten the deal.

More broadly, my research has found that when U.S. presidents host foreign leaders at the White House, those leaders systematically reciprocate by voting more closely in line with U.S. positions at the U.N. General Assembly or by opening market access for U.S. exporters.

A high-level visit can help signal a leader’s domestic strength

If major world powers can extract concessions in exchange for diplomatic visits, what’s in it for the other leader?

My research with Smith suggests that the answer lies in the recipient leader’s ability to secure power at home. No matter the political system, there’s an incentive to fight on the winning side. Dissatisfied elites only want to participate in successful coup attempts, and dissatisfied citizens only want to participate in effective protests.

Candidates are more likely to enter a race against a weak incumbent than a strong one. And voters behave strategically in choosing which candidate to support — either because they expect the winning candidate to directly reward them and their districts with patronage and pork, or because they want to avoid wasting their vote on a candidate with little chance of success.

Since people want to support a winner, any visible, public signal of a leader’s strength is important. And an official diplomatic visit provides just such a signal. That is because only a sufficiently strong incumbent will be able to provide his or her diplomatic counterpart with something of sufficient value as to warrant a visit. When domestic audiences see a high-profile visit, they infer that their leader is stronger than they otherwise might have thought and so become less willing to mount a challenge against her.

So it’s no surprise that leaders are so eager to conduct diplomatic visits with major world powers. Indeed, according to the White House’s memorandum of Trump’s initial phone call with Zelensky, the latter’s first request from the president was for an in-person diplomatic visit.

Archival records provide further documentation of just how desirable presidential visits can be — precisely because of their anticipated effects on domestic stability. A 1958 telegram from the U.S. Embassy in Buenos Aires reported that although Argentina’s President Arturo Frondizi faced the risk of a violent overthrow, “Invitation to visit US also has improved his position.”

In 1951, the chief U.S. representative in Austria suggested that a White House visit with members of the anti-communist governing coalition in Austria “wld be effective demonstration of stability [of] coalition and our own position.” A U.S. diplomat in Seoul wrote in 1964 that a diplomatic visit would “increase ability [of ] govt [to] overcome opposition to its policies and quiet tensions.”

In a quantitative analysis of the historical evidence, my research finds that diplomatic visits substantially reduce the recipient leader’s risk of removal from office.

What makes this visit to the White House unique

U.S. presidents have a range of policy instruments they can use to support their allies’ survival in office and extract international concessions. But diplomatic visits have some particularly attractive features when compared with the other options available.

For one, the president tends to enjoy considerable freedom in choosing whom to visit or whom to host for a visit in the White House. Development aid, commercial agreements, military assistance and other forms of foreign support invariably face greater institutional constraints in their allocation.

The president also bears the costs of a diplomatic visit more directly — both the opportunity costs of his time and any potential reputational costs for diplomatic missteps. A visit can therefore provide a more direct signal of the president’s personal views and priorities. What made Trump’s handling of the Ukrainian case unique, it appears, was his demand for a policy concession that served to benefit the president personally and directly, too.

Matt Malis is a PhD student in the department of politics at New York University.

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