Gas prices have fallen 30% in the last year

It was nigh on one year ago when gasoline crossed a threshold American drivers had never seen before: $5 a gallon.

• Now? We're back to around $3.50.

Driving the news: A slump in the price of crude oil — which accounts for roughly half the price of a gallon of gas — over the last year has helped pull down prices for the fuel.

• A barrel of West Texas Intermediate crude — the U.S. benchmark — is around $70, down by a third over the last 12 months.

The intrigue: Gas prices are also down by about 30% since last June — a move that would typically be expected to improve the mood of American consumers. (Along with the rebound in stock prices from their March lows.)

• But the latest readings on consumer sentiment show there's still plenty of sourness in supply. One key reading shows consumer sentiment falling to a six-month low.

The bottom line: The still-burbling banking crisis, and the building boil around the debt ceiling face-off in Washington seem to be culprits, according to the latest update consumer sentiment from the University of Michigan.