The Air Force was sending a bit of an obvious message to Russia. The Baltic nations are a tad nervous about the expansionistic foreign policy of Russia right now. Russia probably has the capability to overrun the Baltics. But Russia also has some vulnerabilities, such as its dependence on the Baltic Sea for commerce and defense. And the Baltic Sea is particularly vulnerable to interdiction by an offensive mining campaign.
Aerial delivery of mines in World War II was practiced by virtually all sides, particularly in Europe, with Germany attempting to interdict British ports, and Britain similarly attempting to shut down German U-boats.
Possibly the most effective mining campaign in history was the use of B-29s to shut down Japanese shipping in its home waters near the end of the war. Operation Starvation laid a series of minefields around Japan that accounted for an astonishing 670 ships sunk or damaged for the cost of only 12,000 or so mines, and the loss of only 15 B-29s.