Today, Hillary Clinton, John McCain, and Barack Obama issued a joint statement on Darfur: We wish to make clear to the Sudanese government that on this moral issue of tremendous importance, there is no divide between us,” they write. “We stand united and demand that the genocide and violence in Darfur be brought to an end.

The three candidates deplore the violence and condemn Khartoum. They do not say what they will do to stop the killing, yet by issuing the statement they create a marker by which one of them will be judged. All of them deserve our appreciation for the rare show of unity.

Darfur just may be the perfect place to build a national consensus on national security issues. It has three principal advantages for this purpose. First, if Iran is “tiny”–to borrow a word I have heard used to describe it recently–then the western region of Sudan is virtually nonexistent. It is, of course, easy to agree on something not important to us. Second, all Americans feel revulsion because of the rape, slaughter, and genocide. Third, Darfur, although insignificant on its own, brings the critical issues of our time into play.

“There can be no doubt that the Sudanese government is chiefly responsible for the violence and is able to end it,” Clinton, McCain, and Obama state. Yet, as a practical matter, we cannot persuade, intimidate, or punish the abhorrent rulers in Khartoum until we do something about their sponsors, Russia and China. These two states provide arms, material assistance, and diplomatic support to the Sudanese regime. Without their help, the killing stops within weeks.

The three candidates, of course, are not going to have an honest dialogue about the world’s two largest authoritarian powers. But now they have created pressure on the victor to do something about Sudan. And come January–after all, the genocide is “a Day 1 issue”–it is up to the American people to make sure that the next President deals with Darfur by first dealing with Russia and China.