Wars can make, but are much more likely to break, a president’s tenure. They are easy to start, but far more difficult to end successfully.

As the presidential candidates assemble their foreign policy advisory teams, they should carefully consider a president’s most potent power: the use of deadly force by committing American combat troops to battle. At a time when these decisions are increasingly taken without congressional authorization, that power is increasingly vital.

This will be particularly important in the next president’s first year. Since the end of World War II, our presidents have varied widely in how they have considered going to war, particularly at the outset of their time in office. Too often, presidents have committed troops early on in their terms without a full understanding of what it takes to win a conflict, not to mention the commitment to doing so.

Dwight Eisenhower was rare in knowing how to end a conflict. He began his presidency by ending the Korean War on terms that attained all of Truman’s original goals. He also ordered two coups—one in Iran and one in Guatemala. Regardless of their long-term efficacy, neither required U.S. ground troops. Taken together, Eisenhower’s adroit military command was central to his successful eight-year presidency.

John Kennedy stumbled badly in his first year at Cuba’s Bay of Pigs—a failed attempt to topple Fidel Castro. That failure came because he did not fully think through what a successful invasion and regime change would require. Through his handling of the Cuban missile crisis two years later, he restored his public standing, but that crisis would not have taken place had he ousted Castro or, alternatively, had he not so openly provoked Castro and his Soviet allies.

Lyndon Johnson defeated Barry Goldwater in 1964, in part, by painting his GOP rival as a warmonger. Yet, ironically, LBJ’s own piecemeal approach to Vietnam destroyed his presidency. He began the war without clear congressional authorization, pursued an uncertain goal, and prosecuted the effort with military force insufficient to win.

Richard Nixon campaigned in 1968 on a promise to end the war in Vietnam. Yet his end-game meant doubling down on Johnson’s policies. In the end, he lost the war and contributed significantly to his own failed presidency.

In the wake of our withdrawal from Vietnam, Jimmy Carter avoided military conflict. But his presidency was wrecked, in part, by his ineffective use of force adequate to free the hostages taken at our embassy in Tehran, not to mention in countering a hostile and activist Iran.

Ronald Reagan ran on a platform of renewed American military power, with the goal of winning the Cold War by rebuilding American military power. His greatest success was that he did not have to fight a major war. He did invade Grenada and supported a number of anti-communist insurgencies around the world, yet he withdrew U.S. troops from several combat operations. It was the expanded military capacity, not the exercise of that capacity, that marked his administration.

George H.W. Bush may have provided the road map to success. He organized a coalition that liberated Kuwait in 1991 but stopped short of Baghdad. Bush laid out a clear and obtainable goal, secured congressional authorization, and then refused to expand the goal.

Bill Clinton initially stumbled in his use of force—disastrously changing the objectives of a peacekeeping operation in Somalia and hedging on tough rhetoric toward the growing conflict in Bosnia. Eventually, he successfully conducted two operations against Serbia—one in Bosnia and one in Kosovo—that brought peace to the Balkans, while also expanding the NATO alliance. He was less certain in his response to the growing threat of Al Qaeda—especially after the first World Trade Center bombing and the attack on the USS Cole.

George W. Bush, like Clinton, underestimated the threat from Al Qaeda, but in the aftermath of the 9/11 attacks, he successfully toppled the Taliban regime in Afghanistan. But in the preemptive invasion of Iraq in a search for nonexistent weapons of mass destruction, he failed to plan adequately for a lengthy occupation. Bush then expanded the mission to include bringing democracy to a divided and vanquished Iraq. His failure to set explicit and obtainable goals, and to stop when they had been achieved, effectively destroyed his presidency.

Obama abandoned a far too expensive war in Iraq just as it had finally been won. He also denominated the war in Afghanistan a “necessary war,” but never pursued it with the dedication necessary to see it through to victory.

So what does this fairly sorry history of examples tell us about the way in which presidents decide questions of war and peace and how they prosecute wars once begun? What lessons should the next president apply in his or her first year?

Some wars are not optional. Both Al Qaeda and ISIS have declared war on the United States, and our response has been reluctant and ineffective across three presidencies. Such declarations must be taken seriously, and their partisans destroyed or at least rendered incapable of any operations outside of the territories under their immediate control, as quickly and decisively as possible.

Discretionary war questions are far more serious and difficult.

First, the president must be convinced that a vital national interest is at stake and that no course of action short of armed conflict can protect that interest.

Next, the president must be able to articulate that national interest clearly and be confident of our ability to attain victory with the means at our disposal. He or she must also have the courage to follow through once started.

Third, the president must create substantial public support for the course of action proposed, most clearly through obtaining a prior congressional resolution of support.

And, finally, the president must guard against a unilateral expansion of the original goal on the basis of early success.

Once begun, wars should be pursued hard and decisively. Once victorious, we should come home. But absent a reasonable promise of success, wisdom cautions against going to war. And in every instance, congressional support should be sought, in advance if possible. Both the presidency and the country deserve no less.

Slade Gorton was a Republican senator representing the state of Washington from 1981 to 1987 and 1989 to 2001. In 2002, he was appointed as a member of the 9/11 Commission. He is a member of the Governing Council at the University of Virginia’s Miller Center.