WASHINGTON — The day before armed guards from the Turkish president’s security detail violently attacked a group of peaceful protesters here last month, the State Department notified Congress of its intention to license the sale of $1.2 million worth of semiautomatic handguns to the security force.

Two weeks later, with mounting outrage over the episode among American lawmakers and a continuing investigation by the State Department that could lead to criminal charges against some of the guards involved, the future of the sale now appears to be in question.

Though the State Department has not notified Congress if it intends to withhold a license for the sale, it has met resistance from senior lawmakers on Capitol Hill that could stall or even sink the transaction.

The attack has presented the State Department with a particularly thorny challenge, as it balances geopolitical interests with domestic concerns in coordinating a response. American lawmakers have demanded the guards be held to account, while Turkey, a NATO ally and an active partner in the fight against the Islamic State, has all but denied the guards’ role in the skirmish. Several videos show the guards, many with pistols under their jackets, beating protesters.