The negotiations raise questions about what, if any, standards should apply when the United States agrees to trade prisoners.

WASHINGTON — One is perhaps the world’s most notorious arms dealer, a man known as the “Merchant of Death” who sold weapons to terrorists, rebels and militants around the world before finally being hunted down and locked up for conspiring to kill Americans.

The other is a basketball player who got caught with a little hashish oil.

By no measure are they comparable, yet the Biden administration has proposed tradingthe merchant of death for the imprisoned basketball player as well as a former marine held in Russia on what are considered trumped-up espionage charges. In the harsh and cynical world of international diplomacy, prisoner exchanges are rarely pretty, but unpalatable choices are often the only choices on the table.

Whether the swap would go through remained unclear. Secretary of State Antony J. Blinken made the offer public in part to reassure the families of Brittney Griner, the basketball player, and Paul N. Whelan, the former marine, that the administration is doing all it can to free them.