It seems obvious that USAID is an intelligence front (I've encountered a few instances where it was mentioned that someone worked for USAID at the time, while it was simultaneously obvious that it would make way more sense if they were Intelligence), but is there any concrete evidence for that?
*Specially* that we are talking of USAID, on the case of NED for example, things get slightly murkier because then it is a matter of private rather than public record, but it still works as a tool for management of semi-clandestine operations and operations which need plausible deniability from CIA's end, or at least as much deniability as it can muster, tho these days they prefer to work with shell groups and other associated partners such as for example Atlas Network, Radio Free Asia also falls on that category, same with Voice Of America
If you are interested in books both, Killing Hope by William Blum and Legacy Of Ashes by Weiner are very, very, very good authoritative sources on the matter
If you prefer podcasts, Warnerd Radio has a couple very good episodes on the National Endowment For Democracy, tho they both quote excerpts of the books above
Yes, there is concrete evidence--specifically, the Office of Public Safety mentioned by Cyanbird, was an official cover given to CIA personnel to train local and national police forces in puppet countries how to fight a 'countersingurgency'. This included setting up national ID cards to track everyone, NSA style signals intelligence, and extensive use of torture. One of their favorite methods was to use portable US army telephones, as they had a hand crank generator capable of producing enough current/voltage to torture but were unlikely to cause cardiac arrest, they had an obvious non-torture use case so ordering them was not suspicious, and they had very fine wires that could be inserted up the urethra or stuck between teeth to deliver very painful electric shocks to sensitive areas. Dan Mitrione was a USAID OPS guy who was killed in South America in the 70s (Uruguay, i believe) in retaliation for his role in abuse and torture, who was known for adbucting homeless people upon whom his trainees could practice their torture techniques. The 1980 documentary "Inside the Company" about the CIA lays this out very well. It's long but is worth a watch, and I have seen no comparable films exposing this level of CIA activity since. Vietnam and the Phoenix Program is another classic example. John Manopoli was officially working for OPS in USAID, but was in fact CIA, and he first implemented the national ID card program they used to generate the lists of thousands of names of folks to abduct, torture, and either imprison or kill, and he was also instrumental in that part of the plan as well. Almost the only references to John Manopoli are in books about torture in the Phoenix program, or listings in USAID OPS phone books, or a handful of official OPS papers showing he did the same type of work in a handful of other countries.