The oil headlines this week have all been about Iran, but the slowly unfolding disaster in Venezuela may be even more significant.

Less than two weeks before a controversial snap presidential election that would almost certainly give incumbent Nicolás Maduro a six-year term, the country’s main source of export revenue could take another drastic tumble. S&P Global Platts estimates the country’s recent crude production was 1.41 million barrels a day, at least a 30-year low except for a crippling 2002-2003 strike. And over half...