Final answer:
The concern raised by the American Civil Liberties Union (ACLU) regarding Senator Harry Reid's 2013 proposed background check legislation was that the government would have access to databases of gun purchases indefinitely.
Step-by-step explanation:
The concern raised by the American Civil Liberties Union (ACLU) regarding Senator Harry Reid's 2013 proposed background check legislation was that the government would have access to databases of gun purchases indefinitely. The ACLU was worried that this could potentially lead to the government conducting searches on the databases and expanding their use beyond the intended purpose of background checks. This raised concerns about privacy and potential misuse of the collected information.