1.) The modification times on the files point to the use of a FAT file system, which is used almost exclusively by storage devices (such as flash drives).
2.) Analysis of the files released by Guccifer 2.0 claimed to be the Russian hacker who got the files to Wikileaks reveals that they were created at a data transfer rate consistent with a flash drive, but not with an internet transfer."
3.)The NSA would've known the hack was taking place, thanks to the leaks revealed by Edward Snowden, which the NSA has never denied
https://www.c-span.org/video/?475164-1/democratic-national-committee-holds-briefing
The Democratic National Committee held a conference call briefing today about the Republican National Convention and the way forward for the Biden campaign.