Earlier quoted context omitted.
There are only 100 senators, and lots of people track their votes. A senator logging a surprising vote would be asked about it and able to correct the record. Hacking a senate vote wouldn't be much use in the long run.
That is far from clear. Imagine that the famous vote on repealing Obamacare had been done remotely and someone had hacked John McCain's famous thumbs-down vote to be a vote in favor of repeal. Imagine further that before the matter could be clarified with McCain, he had become incapacitated and died. That is a plausible scenario. It only takes one hack at the margins to change the course of history.
It would've been corrected in minutes. McCain knew he was the deciding vote and the media firesform would've alerted him to an incorrect vote almost immediately.
All of these people have large teams monitoring their coverage and managing their PR. A voting mistake would be caught.