A prominent politician who has been a presidential candidate, U.S. senator and secretary of state will be big news this year. But the one to watch isn't Hillary Clinton — at least not yet. Rather, it's John Kerry, whose admirably ambitious diplomatic agenda underscores the welcome ascendancy of diplomacy.

The most immediate and important issue is Iran's potential nuclear weapons program. A brief window of just a few months remains for Iran and major world powers to turn a temporary deal into a permanent solution. For Iran, failure might mean even stricter sanctions, or the renewed prospect of a military strike. For other nations, inaction might mean a nuclear-capable Iran triggering a destabilizing Mideast arms race.

This diplomatic aperture is difficult enough without Congress levying a new round of sanctions. As Kerry himself has said, if a deal cannot be struck, the administration will call for more stringent action. But doing so now would unnecessarily test not just the Iranians, but the global coalition that got Iran to the table.

Most important, failure could propel the United States into yet another Mideast military confrontation. The public and, notably, many in Congress who are pushing for more sanctions on Iran have already rejected a military strike on Syria over chemical weapons.

On another front, Kerry's direct diplomacy has revived the Mideast peace process. There should be no naiveté over how difficult it will be to bridge divides. But finding a solution not only would be good for Israelis and Palestinians but could defuse dangerous regional tensions elsewhere.

Indeed, the region is already reeling over Syria's civil war, which has taken broader, darker sectarian tones and has created a destabilizing refugee and political crisis in nations as far away as Bulgaria. The human toll is staggering: More than 130,000 are dead and up to a third of Syrians are internally displaced or seeking refuge abroad. The opposition to President Bashar Assad, Syria's homicidal dictator, is increasingly radicalized, and the vicious civil war does not seem to have an immediate military solution. This month's Geneva peace conference could be consequential in devising a diplomatic solution to stop the slaughter.

Kerry and other administration officials will also be bargaining with Afghan President Hamid Karzai for a bilateral security agreement that could keep troops in the country past the planned end of combat operations in 2014. This is an often-overlooked but crucial decision not just for America, but for Afghanistan. Iraq's spiraling violence should give both sides pause about what happens when a bilateral security agreement cannot be reached.

These Mideast crises have kept the administration from its planned "pivot" to Asia. Recent flashpoints over disputed islands in the East China Sea, as well as Japanese Prime Minister Shinzo Abe's controversial visit to a World War II shrine reinforce the need for diplomacy to cool the rhetoric and prevent military miscalculations.

Of course, there's upside in Asia, too, as well as with Europe if two huge trade pacts can be inked. But the proposed Trans-Pacific Partnership and Transatlantic Trade and Investment Partnership will need not only global diplomacy but domestic outreach, too.

The Transatlantic pact would also emphasize to Western-leaning Ukrainians that their future does in fact lie with a closer alliance with the European Union rather than with Russia. Russian President Vladimir Putin has been far more personally assertive in courting, or coercing, Ukraine into its orbit. Kerry should earn more frequent-flier miles on his way to Kiev for direct diplomacy.

These are among the known diplomatic challenges. The unknown ones could create crises that also require deft diplomacy. Fortunately, the American people, even if not supportive of President Obama or Kerry, are at least looking for alternatives to the post-9/11 military approach. A recent Pew poll counted the highest number in 50 years for those who say the United States should "mind its own business internationally," and the percentage who say that the country is "more important and powerful than it was 10 years ago" is at a 40-year low.

The real and self-imposed limits of American power come at a time of an increasingly complex geopolitical environment. Domestic support will bolster diplomacy. So, too, would increased involvement from Obama.

The results of Kerry's outreach are uncertain, and no doubt many of his efforts will fall short of the desired outcomes. But the alternatives to direct diplomacy carry greater risks.