“If the result of the referendum is independence, there is going to be war — complete war,” predicts Mudawi Ibrahim Adam, one of Sudan’s most outspoken human rights advocates. He cautions that America’s willingness to turn a blind eye to election-rigging here increases the risk that Mr. Bashir will feel that he can get away with war.

“They’re very naïve in Washington,” Mr. Mudawi said. “They don’t understand what is going on.”

On the other hand, a senior Sudanese government official, Ghazi Salahuddin, told me unequivocally in Khartoum, the nation’s capital, that Sudan will honor the referendum results. And it’s certainly plausible that north and south will muddle through and avoid war, for both sides are exhausted by years of fighting.

Here in Juba, the South Sudan capital, I met Winnie Wol, 26, who fled the civil war in 1994 after a militia from the north attacked her village to kill, loot, rape and burn. Her father and many relatives were killed, but she escaped and made her way to Kenya — and eventually resettled as a refugee in California. She now lives in Olathe, Kan., and she had returned for the first time to Sudan to visit a mother and sisters she had last seen when she was a little girl.

Ms. Wol, every bit the well-dressed American, let me tag along for her journey back to her village of Nyamlell, 400 miles northwest of Juba. The trip ended by a thatch-roof hut that belonged to her mother, who didn’t know she was coming — so no one was home. Ms. Wol was crushed.

Then there was a scream and a woman came running. It was Ms. Wol’s mother, somehow recognizing her, and they flew into each other’s arms. To me, it felt like a peace dividend.

Yet that peace is fragile, and Ms. Wol knows that the northern forces may come back to pillage again. “I don’t want war,” she said, “but I don’t think they will allow us to separate.”

My own hunch is that the north hasn’t entirely decided what to do, and that strong international pressure can reduce the risk of another savage war. If President Obama is ever going to find his voice on Sudan, it had better be soon.