Donald Trump seems like a president without a party. But on at least one issue, he does not operate without a precedent.

President Trump defies conventional ideological descriptions. On domestic policy he has governed not as a conservative but as a populist — leaving untouched popular safety net programs such as Social Security and Medicare and pursuing tariffs to protect American manufacturing jobs.

But perhaps Trump’s biggest departure from Republican orthodoxy has been on foreign policy. And the president he most resembles is a man still respected for his achievements on that front — Richard Nixon.

MARC THIESSEN: TRUMP'S 10 MOST SURPRISING SUCCESSES AFTER TWO YEARS IN OFFICE

President Nixon was perhaps the most famous presidential practitioner of realpolitik — the idea that American policy should be based entirely on protecting American interests. Nixon’s brand of realism led him to pursue détente with the Soviets, an open door to China and an end to the Vietnam War.

And Nixon’s foreign policy efforts did not end with his presidency. As I document in my new book, "After the Fall: The Remarkable Comeback of Richard Nixon," the former president used his intellectual prowess to advise three presidents as they conducted foreign affairs.

Drawing on some never-before-seen documents held by the Nixon family, what I found was a man even more engaged than previously realized, and who was even more successful in shaping world events than previously imagined.

The jury is still out on Trump’s foreign policy. But Trump could do a lot worse than the Nixonian realism he is pursuing.

One of the best examples came during the Reagan-Gorbachev negotiations of the late 1980s. In some ways, President Reagan represented a return to Wilsonian principles in foreign policy — he believed in idealism and wanted to make the world a better place. And so he became obsessed with the Strategic Defensive Initiative, an idea that he believed could make the world safe by providing a shield against offensive nuclear weapons.

But by this point in his presidency, Reagan was routinely seeking advice from his old friend Richard Nixon. Nixon himself had met with Gorbachev and sensed an opening. But he approached the negotiations not with Reagan’s soaring idealism, but with his own deep-rooted realism. Nixon doubted such a technology could work. Yet he never doubted the value of SDI as a bargaining chip. In SDI, Reagan saw a solution; Nixon saw a strategy.

In a 1984 memo to National Security Advisor Bud McFarlane, Nixon suggested that Reagan could “pull a real coup by formally offering at a summit meeting to mutually share with the Soviet Union the results of our research in our defensive outer space programs. This would undercut the position of the critics who claim that we want a shield so that we can use the sword of our offensive capability.”

Nixon believed that Reagan should leverage SDI for negotiating “massive reductions in not only Soviet nuclear forces but conventional forces.”

It worked. Still, the result — the 1987 Intermediate Range Nuclear Forces Treaty (INF) — went beyond Nixon’s realism. It essentially eliminated all nuclear and conventional missiles with short-range and intermediate-range capabilities for both the Soviets and America. Nixon thought Reagan gave up too much in the negotiations. He had wanted the treaty to reduce the nuclear power of the Soviet Union, not of the United States.

With the exception of President George H. W. Bush, the presidents since Reagan have mostly pursued idealistic foreign policies. For largely humanitarian reasons, President Clinton took action against the Serbs, President George W. Bush sought to build a democracy in Iraq, and President Obama waxed poetic in his efforts to encourage the Arab Spring.

Enter Trump — a very different president with very different foreign policy ideas. He criticized the Bush Doctrine during the 2016 campaign, and he has governed as a realist in the Nixon mold on foreign policy.

When evidence emerged that the Saudis had murdered an American journalist, the Trump administration was careful not to sever relations with a Middle East ally. He overruled military leaders (including his secretary of defense) and announced plans to withdraw troops from Syria. And he even announced he was withdrawing the United States from the INF Treaty — the same treaty that Reagan signed and Nixon worried about.

CLICK HERE TO GET THE FOX NEWS APP

Successful or not, Trump’s forays on the world stage represent a clear return to the realism of Nixon. And the similarities are not lost on the current president. One of the first items he placed in the Oval Office in January 2017 was a framed letter written to him by one his favorite presidents — Richard M. Nixon. Nixon’s letter said that Pat Nixon had seen Trump on television and predicted “whenever you decide to run for office you will be a winner!”

The jury is still out on Trump’s foreign policy. But Trump could do a lot worse than the Nixonian realism he is pursuing.