President Trump’s comments in a phone call with Ukrainian President Volodymyr Zelensky in July have prompted the House of Representatives to launch an impeachment inquiry.

Trump reportedly pressured his Ukrainian counterpart to investigate Joe Biden and the former vice president’s son, Hunter Biden, who served on the board of Burisma, a Ukrainian gas company. He also offered to enlist U.S. Attorney General William P. Barr and his personal attorney, Rudolph W. Giuliani, in that effort.

Trump’s action — far from the first controversy the president has created while interacting with a foreign counterpart — appears to be a flagrant abuse of power. But it is one enabled by a system that extends presidents enormous freedom in conducting personal diplomacy with limited transparency and few checks on their power.

This system of leader-to-leader diplomacy has become a key aspect of conducting foreign policy since the early 20th century. Although this can create opportunities to make peace, it can also exacerbate dangers, as Trump has vividly illustrated. Given those newly apparent downsides, we must ask whether this 20th-century model of personal diplomacy should finally be retired.

When designing our constitutional system of checks and balances, the Founding Fathers never could have imagined the degree to which modern presidents personally interact with foreign leaders.

In the nation’s first 150 years, presidents had little direct contact with heads of state and government. Presidents set the general strategy for American foreign relations, but the conduct of diplomacy was mostly left to the State Department.

This started to change in the 20th century. Technological improvements in communication and travel made direct and frequent contact between world leaders possible. More importantly, international crises, increasing presidential desire for control and domestic political incentives combined to make personal presidential diplomacy an attractive tool.

Woodrow Wilson was the first U.S. president to interact extensively with foreign leaders. In 1919, he went to the Paris Peace Conference after World War I. Though feted by European governments, his trip provoked a firestorm of criticism back home. Some believed it was unconstitutional. Critics worried that if America’s leader was exposed to Europe’s monarchical pomp and wily leaders, the nation’s republican simplicity was at risk.

Undeterred, Wilson engaged his foreign counterparts in private talks and negotiations that ultimately produced the Treaty of Versailles. But the Senate rejected his diplomatic handiwork. Many senators were upset Wilson did not seek their counsel. The treaty’s fiercest critics argued that he had negotiated an agreement that threatened American sovereignty and security.

After Wilson’s failure, it would be two decades before another president embraced personal diplomacy in the same way. In a world beset by crisis, Franklin D. Roosevelt understood the benefits of interacting with his counterparts, believing it helped clarify positions and harmonize relations. He frequently engaged foreign leaders, most notably during World War II with British Prime Minister Winston Churchill and Soviet leader Joseph Stalin.

Many praised Roosevelt’s style of diplomacy, but others saw his secretive talks with foreign leaders as dangerous and incompatible with the nation’s democratic principles.

This critique only intensified after Roosevelt’s sudden death in 1945. As U.S.-Soviet cooperation began to crumble, the agreements Roosevelt made with Stalin at the Yalta Conference came under increasing scrutiny. For the most partisan Republican critics, Yalta became synonymous with treason because no one knew specifically what Roosevelt had agreed to thanks to the secretive nature of the talks, which fueled speculation. Roosevelt exacerbated the situation by overselling Yalta to the American public and keeping some agreements secret — after saying there were no such arrangements. These revelations made the administration appear deceptive and tainted Yalta as a sellout of Eastern Europe that laid the foundation for the continent’s Cold War division.

Even non-partisans were concerned about Roosevelt’s informal management style and the personal nature of his diplomacy. He had left his vice president, Harry S. Truman, in the dark, which became pivotal after Roosevelt’s death because it made the continuity of government policies difficult — a dangerous situation in wartime. Truman eventually learned of Roosevelt’s personal dealings from Harry Hopkins, an unofficial Roosevelt adviser who attended the major wartime conferences.

Responding to this anxiety over Roosevelt’s handling of foreign policy, Congress established the National Security Council in 1947. The aim was to coordinate the national security apparatus more efficiently and produce a more systematic decision-making process by presidents. In the following decades, presidents would use the council in various ways to suit their needs, but it never eliminated the personal element of the nation’s foreign affairs.

If anything, personal diplomacy became an increasingly integral part of Cold War foreign policy. Proponents argued it could promote understanding between leaders and reduce tensions. But it also provided presidents more control and fewer constraints. Directly engaging a foreign leader allowed them to sidestep the slow-moving national security bureaucracies that were often resistant to new approaches and prone to leaks. When Ronald Reagan, for example, decided it was time for serious arms control talks with the Soviet Union, he used personal diplomacy to sideline the bureaucrats and hard-liners in his administration.

The freedom that personal diplomacy afforded presidents also meant risks. What prevented a president from saying or agreeing to something improper?

This concern rose to the fore during the Watergate era. In his first term, Richard M. Nixon used personal diplomacy to great effect, going on historic journeys to China and the Soviet Union.

But in 1974, at the height of the scandal, Nixon embarked on a heavy schedule of foreign travel, visiting Europe, the Middle East and the Soviet Union. These trips raised alarm back home: Would a weakened president make harmful concessions to foreign leaders? Would a desperate president agree to something not in the national interest?

This didn’t happen, but that was because of Nixon’s restraint, not because of any safeguards.

Reagan’s 1986 summit with Soviet leader Mikhail Gorbachev in Reykjavik, Iceland, presented a different concern. On the last day of talks, a well-intentioned Reagan suggested the elimination of all nuclear weapons. This came as a shock to his advisers and to other world leaders who relied on America’s nuclear arsenal for their defense. Eliminating nuclear weapons would have marked a radical change in America’s security strategy. Yet Reagan had consulted no one before proposing it.

Similarly, Trump often abruptly shifts American policy with little consultation with his aides, U.S. allies or Congress. And legally, he’s free to do so. “Putting it brutally, Article II gives the president the authority to do, and say, and pledge, awful things in the secret conduct of U.S. foreign policy,” Harvard law professor Jack Goldsmith tweeted. “That is a very dangerous discretion, to be sure, but has long been thought worth it on balance.”

A big part of what has made this trade-off worthwhile is luck. The United States has been fortunate to have, for the most part, presidents with a sense of what was inappropriate behavior. Even Nixon, who was willing to engage in egregious misdeeds, resisted temptation in his conduct of diplomacy during the darkest moments of his presidency.

With Trump, however, it seems as though that luck has vanished.

There’s no easy fix. Congress could try to limit presidential power in this area, but there is no guarantee that restrictions would improve U.S. foreign policy. Diplomacy requires flexibility and discretion. Limiting presidents in their interactions with world leaders might hinder this diplomatic dexterity and could be harmful to the nation’s interests. The only real safeguard is the American voter, who must choose candidates with the integrity and honesty to be diplomat-in-chief — and reject those who demonstrate that they lack it.