I recently delivered a major foreign address at the University of Chicago, in which I highlighted the need for a departure from our foreign policy adventurism—and the need to demonstrate American strength through economic trade and through diplomacy.

Although President Obama ran for office in 2008 on a promise to get America out of Middle Eastern wars, under Secretary of State Hillary Clinton, his administration continued a series of policies of regime changes, particularly in Syria and Libya.

First, let’s be absolutely clear. The president’s first and most solemn responsibility is to keep us and our freedoms safe, especially from foreign attack. If the government does nothing else, it must do that.

Keeping us safe means having a military capability that is unquestionably second to none. Ronald Reagan was onto something when he spoke of “peace through strength,” and even in our most severe budgetary constraints, we have the resources to maintain the greatest defense on the planet.

But that doesn’t mean we cannot reduce military spending. In fact, we must.

Where the debate comes into play is what we expect our military to do. The best word to describe my approach to military interventions abroad is that I am a skeptic. As president, I would not need to be talked out of dropping bombs and sending young men and women into harm’s way. I would be the president who would have to be convinced it is absolutely necessary to protect the American people or clear U.S. interests. I will be the skeptic in the room.

And there is good reason for skepticism. Just look at the past fifteen years. I supported going into Afghanistan after 9/11 to deal with Al Qaeda and its Taliban hosts. We were attacked, and we attacked back. But seven months after we sent our troops to Afghanistan, Al Qaeda had scattered to the winds and the Taliban had been removed from power. Al Qaeda was gone, but we stayed . . . and stayed . . . and stayed. We’re still there.

We’ve been on every side of the conflicts in Afghanistan that have defied resolution for generations. You all are too young to remember, but there was a time when we were fighting on the same side as Osama Bin Laden against the Soviets, who learned the hard way the futility of engaging in Afghanistan’s tribal wars and politics.

Although the oft-claimed idea that we actually armed and supported bin Laden has never been documented, we were, however, arming and supporting those on the same side as him in the resistance.

We accomplished our mission in Afghanistan, and we should have stopped there. Today, too many lives and too many dollars later, the Taliban is returning to Afghanistan. And if we were to mount another surge, remove them, and stay there another fifteen years, the same thing would happen as soon as we left—unless and until Afghanistan takes its own destiny into its own hands.

Likewise, it is difficult, if not impossible, to identify an instance where our military interventions and regime changes in the past fifteen years have improved the lives of anyone. Iraq. Yes, Saddam Hussein was a bad guy. No question about it. But are the Iraqi people better off today because we decided to take him out? Are we safer here in America? No.

In fact, let’s not forget that, as bad as he was, Saddam was the roadblock standing in the way of Iran’s rise as a real threat to the rest of the region. Removing him freed Iran to pursue its ambitions and turn its attentions elsewhere. An unintended consequence, for sure. But a real one we must admit, and which should have been anticipated.

And let us also not forget that, prior to our invasion of Iraq, Turkey was a strong and reliable NATO ally in the region. But that relationship went south in a big way when we invaded Iraq, an action Turkey opposed for its own reasons. Today, as we deal with ISIS and Syria, we wish we had the old Turkey and our strong alliance with them back.

As for Iraq itself, well, it is obviously a tragic mess. Saddam was horrible, but is what we replaced him with any better?

Libya. Same song, different verse. We used our military to help overthrow Qaddafi. Again, a bad guy and, by most standards, a war criminal. But what took his place? Did we have a plan? Did we consider the potential consequences, with which we are living today?

I could go on, but the lesson is clear. Is it our fault that chaos has consumed nations such as Afghanistan, Iraq and Libya, or that violent extremists have found homes in the wake of our interventions? No. It isn’t our fault alone. We had good intentions, but we intervened with no clear vision of the outcomes, and frankly, with no clear vision as to the overall U.S. interest, which should be the guiding principle.

I’m a chess player. Making a move without looking ahead to your opponent’s moves or even what your own next move might be usually doesn’t turn out well in the end. Our foreign policy, or lack of it, over the past fifteen years, has been a series of erratic chess moves, and the match isn’t going well.

We need a chess player in the White House. More important, we need a policy guided by principle, not politics.

The first and overriding principle is that our foreign policy and military actions must support clear U.S. interests. That seems obvious, but in recent years, it has not been the case. Our interests are our lives, our property and our freedom. They are not necessarily a desire to shape the world in our own image or to pick winners and losers in civil wars on the other side of the globe.

The second principle is that we must expect and demand that other nations shoulder the responsibility for their own defense and economic well-being. We are broke. We cannot any longer subsidize the national defense and economies of other nations. Yes, we will honor our commitments to NATO and other agreements, but other countries around the world have grown too dependent upon U.S. military power.

The U.S. military exists, first and foremost, to defend the United States and U.S. vital interests. If our actions sometimes help others, that is a useful byproduct. But it shouldn't be confused with the U.S. military's—and the U.S. government's—core mission. Instead, we should expect other countries to defend themselves and their interests. If they did so, they would have greater capabilities for dealing with local problems before they become global ones. We should want more countries who share our values to be acting to defend those values, not paying us to do it for them.

Today, U.S. military spending accounts for roughly one-third of total military spending of the entire world, exceeding the combined total of the next seven largest military budgets including those of Russia and China. Here at home, military spending accounts for almost half of all discretionary federal spending.

U.S. taxpayers are picking up the tab for far too many others around the world, and we simply cannot afford it.

Third, we must not ask our military to engage in conflicts without a clear mission and clear authorization. In Afghanistan and Iraq, what were our objectives. When could we possibly know when “mission accomplished” arrived? In 1991, when President George H. W. Bush ordered our troops to push Saddam and the Iraqi forces out of Kuwait, with the support of a broad coalition, they had a clear objective, achieved that objective in a matter of weeks, and the president resisted the temptation to push on into Iraq and topple Saddam Hussein.

Many second-guessed that decision, but it was a clear objective, a clear mission, and had a firm conclusion. That is what our military deserves, and what they expect. Our last two presidents have not provided that certainty to either our military or to the American people. Rather, we have engaged in conflicts with no clue as to the outcome or the “end game.” Lives have been lost, hundreds of billions spent, and vacuums created that have made the world more dangerous.

As for authorization, whatever happened to the constitutional notion that Congress should declare wars? The interventions that have cost thousands of lives and trillions of dollars over the past fifteen years have been conducted on the basis of authorizations passed by Congress in the aftermath of 9/11. Congress has since allowed the president to conduct “executive wars” while avoiding their responsibility to place a check—or an approval—on those wars. Yes, they have continued to fund them, but as far as casting the tough votes to drop bombs or deploy our young men and women, Congress has been AWOL.

We need to honor the War Powers Act and force both Congress and the president to only engage in war with a clear authorization from both the Executive and Legislative Branches. As president, I will honor the War Powers Act, without hiding behind dubious legal opinions from my own lawyers.