Failure of political class caused recession, not Buhari

Was it Buhari that caused the international price of crude oil to fall in 2015? Are you not aware that Nigeria has been a mono product economy and that any fluctuation in that price would prove devastating to an economy overly dependent on it? This is unlike the US where Obama was able to assure the US that they wouldn’t be seriously hurt by the fall in crude oil prices, because according to him the US was not dependent on crude oil.
Was it Buhari that told the political class not to save adequate amounts of oil revenue for decades? This is unlike Norway that managed to save $800 billion and thus escaped the devastating impact of the fall in crude oil prices.