By the turn of the 21st century, it was clear that a new approach to the use of American power to protect our national interests and values was necessary.

At the risk of some over-simplification, by the end of former President George W. Bush’s second term, essentially two lines of thinking had emerged. On the right was a preference for the use of “hard power” — the use of military force and intervention to protect U.S. interests. On the left was a growing bias against military intervention of any kind and in favor of “soft power” — economic aid and incentives on human rights and democracy. And recently, we have seen the libertarian right, led by Sen. Rand Paul (R-Ky.), appearing almost always to oppose both hard military power and soft power of foreign aid and economic development.

Former Secretary of State Hillary Clinton, in partnership with her boss, President Obama, came up with a mix of hard and soft, calling it “smart power,” with the appropriate mix between the two driven by specific facts and circumstances.

“The president-elect and I believe that foreign policy must be based on a marriage of principles and pragmatism, not rigid ideology,” she said at her January 2009 confirmation hearings. “We must use what has been called ‘smart power,’ the full range of tools at our disposal — diplomatic, economic, military, political, legal, and cultural — picking the right tool, or combination of tools, for each situation. With smart power, diplomacy will be the vanguard of our foreign policy.”

In a recent op-ed, former Joint Chiefs of Staff Gen. Hugh Shelton wrote about Clinton’s tough words and attitude concerning Russian President Vladimir Putin’s intentions — calling him a “KGB agent,” defined as someone who “doesn’t have a soul.” Shelton also reminded us of Clinton’s use of effective diplomacy with Putin, identifying common interests with an adversary — incenting Russia to agree to new United Nations sanctions on Iran, as well as cooperation on anti-terrorist efforts, including reaching a historic “lethal transit” agreement, which allowed U.S. military planes to transport lethal materials over Russia to Afghanistan.

Or take Clinton’s leadership in supporting and helping the Treasury Department’s Office of Foreign Assets Control to implement tough economic sanctions against Iran. These policies constitute a good example of “smart power” in attempting to deter Iran’s development of a nuclear weapon while not eliminating a military option.

“I voted for every sanction that came down the pipe against Iran,” she said recently in a speech to the American Jewish Congress, referring to her years as a senator. “We went after Iran’s oil industry, banks and weapons programs. We enlisted insurance firms, shipping lines, energy companies, financial institutions, and others to cut Iran off.”

Thanks in large part to her and Obama’s leadership, the European Union, the U.N., and nations around the globe joined in to make the U.S.-initiated sanctions regime effective. National Public Radio reported that “there’s widespread agreement that sanctions have worked [against Iran], squeezing Iran financially and bringing its leaders to the negotiating table. Iran’s economy is, by any measure, in terrible shape.” Says Barbara Slavin, an Iran analyst for the Atlantic Council, in the piece, “The cost of living has gone up so fast for Iranians that they are absolutely stunned, and people are simply not able to maintain the middle-class lifestyles they are used to.”

While Clinton has supported the Obama administration’s efforts to negotiate a pullback from Iran’s effort to develop a nuclear weapon, she said in a recent speech that she remains “skeptical that the Iranians would follow through and deliver. I have seen their behavior over the years. But this is a development that is worth testing.”

“We want to give space for diplomacy to work,” she said (soft power). “If it does not, then we can always and we will, put on additional sanctions … and yes, we will explore every other option. And let’s be clear, every other option does remain on the table.” (hard power).

In short, soft + hard = smart, and it could be one of Clinton’s most enduring doctrines and legacies of her leadership at the State Department in the early years of the 21st century.

Davis served as special counsel to former President Clinton and is principal in the Washington D.C. law firm of Lanny J. Davis & Associates, and is Executive Vice President of the strategic communications firm, Levick. He is the author of a recently published book, Crisis Tales:  Five Rules for Coping with Crises in Business, Politics, and Life.