Count on it: When it comes to foreign policy, two-term presidents -- and even most one-term presidents -- will change course along the way. Since 1933, only two have not: Lyndon Johnson, who rode the Vietnam War all the way down, and Barack Obama. That's not a good sign.

Consider the record. When Franklin Roosevelt entered the White House in 1933, he began by torpedoing the World Economic Conference and accepting neutrality legislation. But over the 1930s, he moved from isolationism to leading the United States into the Second World War.

At first, Harry Truman drew down U.S. military strength rapidly after 1945, especially in Europe. But as the Cold War began to take shape, he reversed course and brought the U.S. into NATO.

Dwight Eisenhower moved from rejecting summits with Soviet leaders and opposing Western intervention in the Middle East, to holding summits and intervening himself. Jimmy Carter couldn't accept the Soviet Union was a problem, until it invaded Afghanistan.

Ronald Reagan confronted the Evil Empire, but after 1983, decided the time was right to negotiate with it. George W. Bush entered office saying that the U.S. military should be doing less in the world, but 9/11 changed many minds, including his.

The only real exception to the rule is Johnson, who hated the Vietnam War, but who got us into it and was never willing to get us out. True, the changes don't happen for the same reason. Sometimes, presidents are wrong and recognize it, like Carter.

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Other times, presidents, like John F. Kennedy, deliberately reverse the policies of their predecessor, only to find out after a few years that the previous guy wasn't entirely wrong. At times, as with 9/11, the world changes, and the president changes as a result.

And sometimes, as with Reagan, their initial policies work, which allows them to move on to a new part of their strategy. But in most cases, change isn't a sign of failure. It's a sign of success, of adaptation, or at least of learning.

Nor is it a sign that presidents are giving up on their goals or their core beliefs. With the exception of genuinely clueless presidents like Carter, most changes are about means, not ends.

That's because it's not reasonable to expect presidents to change who they are. If they were so easily changed, they wouldn't have become president. But it is reasonable to expect them to look at how they're doing, at the world around them, and adjust accordingly.

Obama stands out because he is the same man we first elected in 2008 -- which is fair enough -- with the same foreign policy. Unlike almost all of his predecessors, he's not changed significantly. Unfortunately, that's a lot less reasonable.

Yes, there have been tactical adjustments. Obama talks less about the United Nations now than he did in 2009. But the first thing he did when he came into office was to reach out to Iran; over six years later, we're still riding that train.

Obama wanted to "reset" relations with Russia. He still hankers after the same thing, as evidenced by his comments about Vladimir Putin after the Iran deal. He wanted to reduce U.S. involvement in the Middle East, and reach out to adversarial regimes like Cuba's diplomatically, so that he could focus more on domestic policy. No change there, either.

I don't agree with these policies. But what is remarkable to me is the consistency with which Obama has pursued them. Obama has a perfect right to have his values. But precedent suggests that presidents who don't adapt how they apply their values are regarded by history as failures.