But Trump’s behavior makes sense in light of my research showing that presidents face strong incentives to campaign as isolationists — and to govern as hawks.

Here’s the background

My theory of presidential behavior is based on two previous findings from political science. First, from Richard Neustadt and Stephen Skowronek to Terry Moe and William Howell, scholars have shown that presidents have incentives to exercise and expand the powers at their disposal. Since foreign policy is an area where presidents face few constraints, they are especially prone to intervene with military force abroad — regardless of their previous campaign rhetoric or party ideology.

Second, as Frances Lee has shown, parties see politics as a zero-sum game. I show that when they control the White House, they often justify their own president’s interventionist behavior — but when they are in opposition, they criticize foreign intervention.

AD

AD

Thus, in a presidential campaign — all other things being equal — the challenger’s party is usually less interventionist than the incumbent’s party. But if the challenger wins, he or she will probably pursue a foreign policy as interventionist as that of the predecessor they criticized in the campaign. At that point, the two parties will change their positions on foreign policy accordingly.

This historical pattern goes back at least to 1900

To test this theory of presidential and partisan behavior, I examined U.S. presidents’ foreign policy actions and the two major parties’ ideologies from 1900 to 2016. Almost every president pursued an interventionist foreign policy regardless of previous ideological commitments, and in almost every instance the two parties changed their views about foreign intervention as predicted.

AD

AD

For example, at the turn of the 20th century, Republicans in control of the presidency were significantly more internationalist and hawkish than their Democratic counterparts. They nominated candidates like Teddy Roosevelt, who called for the U.S. to “carry a big stick” and exercise “an international police power.” Democrats, on the other hand, criticized Republican “militarism” and “imperialism,” and nominated candidates like the isolationist populist William Jennings Bryan.

But after Woodrow Wilson took the presidency in 1913, Democrats gradually began moving in a more internationalist and hawkish direction. As Wilson moved the United States closer toward intervening in World War I, Bryan resigned as secretary of state.

At the same time, an isolationist faction emerged in the Republican Party. The GOP turned away from decades of internationalist campaign rhetoric and governance. Strangely enough for those who lived through it, Republican Warren G. Harding won the 1920 election by criticizing Democratic interventionism.

AD

AD

More recently, 2000 Republican presidential candidate George W. Bush promised to have a “humble” foreign policy that would be “judicious in its use” of the U.S. military, and criticized Vice President Al Gore and the Democrats for intervening in places like Haiti and the Balkans.

Meanwhile, the 2000 Democratic platform boasted that “the Clinton-Gore administration … has ensured that America is prepared to fight alongside others when we can, and alone when we must. We have defeated attempts to cut our defense budget irresponsibly.” This rhetoric only became remarkable when the two parties switched positions after Bush became president.

To be sure, presidents and their parties are not entirely ignorant of what they said in the past. They often justify these foreign policy reversals by making distinctions between how they are intervening in foreign affairs and how their predecessors did so. Nonetheless, if we look at the course of U.S. history, we find a general pattern of parties becoming more or less interventionist on foreign policy depending on which controls the White House.

AD

AD

Party members change their views as well

It’s not only the parties’ politicians and leaders who change ideology depending on who’s in or out of power. Ordinary voters switch positions as well.

In the postwar era, the American National Election Studies (ANES) have regularly asked Americans whether they agree or disagree with the following statement: “This country would be better off if we just stayed home and did not concern ourselves with problems in other parts of the world.”

As the figure below shows, Democrats’ and Republicans’ attitudes change in ways that closely track changes in which party controls the presidency.

In 1952, after 20 years in which Democrats controlled the presidency, more Democrats than Republicans – by a margin of 13 points – gave the interventionist response. But during the Eisenhower administration, Democrats and Republicans changed positions. Over the next few decades, whenever a Democrat was president, the gap between the two parties narrowed. Whenever a Republican was president, the gap widened again.

AD

AD

By 1992, after controlling the presidency for 20 of the previous 24 years, Republicans had become more interventionist than Democrats by an astounding margin of 14 points.

During the Clinton administration, that margin evaporated. By 1998, a greater percentage of Democrats than Republicans were rejecting isolationism.

Now Trump fits the pattern

The past two decades have followed this same pattern. Republicans were significantly more hawkish than Democrats during the Bush administration. But during the Obama administration, the two parties gradually switched again. For example, in the 2008 NES survey, 75 percent of Republicans and just 65 percent of Democrats gave the interventionist response. By 2012 and 2016, the GOP number fell into the 60s, while in 2016 the Democratic number had jumped into the 70s.

AD

AD

It’s no wonder, then, that in the 2016 primaries, the GOP nominated a less interventionist candidate like Trump. And it’s no surprise that Trump is beginning to govern as an interventionist. Now sit back and watch whether the two parties change their foreign policy views to fit.