The current Ebola outbreak in the Democratic Republic of Congo is only the second-largest in history, but undoubtedly the most frustrating.

Scientists are fairly certain they have the medical tools needed for victory: one vaccine that appears to work about 98 percent of the time, another that has worked well in monkeys, and four therapies that may block the virus if they are given early enough.

Instead, scientists are being thwarted by the nightmarish conflicts and politics of eastern Congo. Health workers have been murdered, treatment centers have been torched, rumors have repeatedly outwrestled the truth. An overwhelming sense of divisiveness and fear has undone almost every effort to save the stricken and protect the vulnerable.

Three previous Ebola outbreaks have demonstrated how a response can succeed — or how, in an atmosphere of suspicion, it can go badly wrong.