American drivers just caught a break they haven’t seen in months. The national average price of gasoline dropped to $3.997 per gallon on June 14-15, slipping below the psychologically significant $4 mark for the first time since mid-April, according to GasBuddy.

The catalyst isn’t a new drilling boom or some miraculous leap in refinery efficiency. It’s diplomacy. Specifically, growing optimism around a preliminary agreement between the US and Iran that could reopen the Strait of Hormuz, one of the most critical chokepoints for global oil shipping.

Why the Strait of Hormuz matters this much

Crude oil prices fell over $4 per barrel in early trading sessions as markets digested the possibility of smoother oil flows through the strait. Gasoline prices, which track crude with a short lag, followed suit.

Nearly half of US states are now reporting average gasoline prices below the $4 threshold.