Syria is not the key to resolving any of the Middle East’s crises—not Iraq, Lebanon, Israel-Palestine, or Iran—but it has the power to stymie progress on all of them. Geography alone makes Syria, with its borders with Israel, Iraq, Lebanon, and the Kurdish region of Turkey, central to Middle East peace. Add to that the long-standing, albeit highly unusual, relationship between the secular Sunni regime in Damascus and the Shiite mullahs in Tehran, and Syria’s importance is indisputable.

Of course, there are plenty of reasons to view President Bashar al-Assad’s regime with suspicion. Syrian-backed assassinations have taken Lebanon to the brink of collapse, and Israeli airstrikes recently raised rumors of a secret nuclear program. But consider that the same government has opened an embassy in Baghdad, taken in more than a million Iraqi refugees, made an appearance at the Annapolis Middle East peace conference, and appears to have cracked down on the passage of foreign terrorists into Iraq in recent months. Yet, Washington has slammed the door on the possibility of a relationship.

The Bush administration’s “they know what they need to do” school of diplomacy, demanding its own desired outcomes as preconditions for talks, has failed utterly with the Syrians, as it has everywhere else. From Cuba to Iran, shunning regimes the United States doesn’t like has never achieved anything other than the deepening of mutual mistrust. That’s why it’s time for the next president to reopen the road to Damascus.

Syria has signaled for several years that it wants a relationship with the United States. A year ago, Assad’s top legal advisor reportedly told participants at an international gathering that “negotiations mean...