It seems to me as if journalists cannot tell the difference between these two words. They aren't even homonyms!
Defuse. That's what you do with a bomb. More metaphorically, that's what you do with a dangerous situation - you calm it down and remove the detonator and explosive.
Diffuse. When you add a drop of ink to a glass of water, the ink diffuses through the water, until eventually it's all mixed in.
Do, you do not "diffuse" a dangerous situation. You defuse it.
Please get these straight.