Having worked for six secretaries of state over 20 years, I have a pretty clear sense of what makes a good one — and with the economic and financial crisis overshadowing foreign policy these days, the selection of an effective secretary of State is more imperative than ever.

In the last 30 years, I believe we've had only two truly consequential secretaries of state. James A. Baker III (whom I worked for and admired) and Henry A. Kissinger, with all their imperfections and detractors, stand out well above the others. They had different personalities, confronted different circumstances and succeeded and failed in different ways. But they embodied four important qualities that helped them succeed:

The right persona. Freud may have been overly deterministic when he talked about anatomy as destiny, but when it comes to what it takes to be an effective secretary of state, he wasn't far off the mark. The nation's top diplomat needs to be actor, teacher, tactician, intimidator and confidant. When an American secretary of state walks into the room his or her interlocutors need to be on the edge of their seats, not comfortably situated in their chairs wondering how best to manipulate the secretary.

Kissinger and Baker impressed Arabs and Israelis with endurance and stamina in negotiations. Both were actors who could yell and threaten to abandon the process (Baker at least twice with Syrian President Hafez Assad and Israeli Prime Minister Yitzhak Shamir; Kissinger at least once with Assad), yet they could also reassure. That mix of keeping their interlocutors off balance but reassured proved indispensable to successful diplomacy.

The president's confidence. The assumption that a new president will appoint a secretary of state who is close to him and has his confidence is not always accurate. Of the six secretaries I worked for, only one — Baker — had a truly close relationship with his president. Yet this relationship is crucial. You cannot expect to do serious diplomacy abroad, or in the perilous world of Washington, without knowing that the president has your back, will not allow domestic interest groups to undermine you or permit his other advisers to do so.

Baker's relationship with President George H.W. Bush was very special — that of a close friend, even, it sometimes seemed, a younger brother. Kissinger's relationship with Richard Nixon was more distant and competitive, but Nixon recognized Kissinger's talents and gave him room to navigate.

It takes America's friends and adversaries about five minutes to figure out who really speaks for the White House and who doesn't.

A negotiator's mindset. Teenagers talk on the phone, beavers build dams and secretaries of state manage crises and solve problems. This means having a smart and tough view of the world, seeing how America's ends and means fit together, and knowing how to make them do so. There is little room for ideologues here, or for minds that lack the capacity to reconcile the yes and no of international relations with all the contradictions that impose themselves on diplomacy.

The negotiator's mindset — the intuitive capacity to see where the deal is and to bring it about — is critical. It's not learned. Baker was a lawyer by training; Kissinger an academic. Both were terrific negotiators who succeeded far more than they failed.

Deviousness and toughness. This last point may not be politically correct, but effective secretaries of state are manipulators. Deception is sometimes required, and they maneuver constantly, trying to figure out what's necessary to succeed and how to use incentives, pressure, arm twisting and, when necessary, untruthfulness (by omission or commission) to manage a crisis or close a deal.

Baker and Kissinger were not sentimentalists. To close their Middle East deals, they trash-talked Israelis to Arabs and Arabs to Israelis. They threatened when they had to and conceded when they had to, never losing sight of the objective or of a back door to get out. Nice secretaries of state are usually ineffective secretaries of state.

Of course, even an all-star secretary of state cannot guarantee a successful foreign policy. The president's persona, other policy priorities, sheer luck and the uncontrollable flow of events matter more. But an effective secretary who can deal with crises and exploit them as opportunities is critical.

Whether or not President-elect Barack Obama selects Sen. Hillary Rodham Clinton, D-N.Y., or some other talented candidate, it is essential that that person possess many of the qualities that made Kissinger and Baker so successful.

Aaron David Miller, a public policy scholar at Woodrow Wilson International Center for Scholars, worked as an adviser on the Middle East for six Democratic and Republican secretaries of state. He wrote this commentary for the Los Angeles Times.