” Congress knows the FBI was aware of a breach by foreign actors from Clinton’s server ..”
I thought her server wasn’t hacked? I thought her server didn’t contain any classified information? I thought she only deleted emails concerning yoga and wedding plans?
In the common parlance, "hacking into a server" means basically logging on to that system and accessing the contents, or otherwise manipulating that system. Sometimes, but not always, a "hacker" will leave evidence behind in the form of access logs or other changes. A skilled hacker erases his tracks. All the FBI said was that it found no evidence that an unauthorized (and non-local to the machine) person gained access to Clinton's private server.
However, that form of "hacking" is not the only way to get the information. The senders and recipients of transmission are other places the information is available; and the information is transmitted and can be copied by anybody who handles the transmission, or who has access to the transmission. NSA vacuums 100% of the transmissions that cross national boundary, and likely 100% of transmission that is domestic.