Then you have to define the term "hacking". The voting machines were not connected to the internet, and the only possible way to hack them is to do it manually for each of the machines. Do you think that it is possible?
That's a different issue, and yes it is not only possible, but Russia tried that too
This is what the leak from Reality Winner (her actual name) was about...
The leak showed Russia not only hacked into the database of the company who makes the voting machines, but that they tried phishing emails (and more?) against people who had access to the machines
So yeah, Russia at least tried to compromise the voting machines themselves, but nobody knows whether they were successful, because zero states audited/recounted the election results
This leak is only about a week old, so no telling how long congress etc has known about it
http://www.nydailynews.com/news/national/russia-hacking-worse-reality-winner-leaks-show-senator-article-1.3225906Moscow's largest foreign intelligence agency — targeted employees at an electronic voting vendor in August. At least one employee was likely compromised, the report said.
Hackers then used info from the company to target more than 100 local government email addresses by pretending to be from Florida-based VR Systems, the NSA report allegedly said.
fake emails the hackers sent from VR Systems contained booby-trapped Microsoft Word documents designed to give up control of a computer's functions and allow "persistent access" to deliver more malware, the NSA report said.
The intelligence report did not say whether those emails were successful in compromising local officials' computers and systems. But Intercept reporters pointed out that a registration system malfunction in Durham, N.C., which used VR Systems, caused long lines and confusion at some polling places. A deputy director for the Durham County Board of Elections said the company's software was not the cause of problems.
The leaked documents shed new light on alleged interference efforts by Russia close to the election, with the disclosure saying the hacking "may have breached at least some elements of the voting system, with disconcertingly uncertain results."