>They vote for everything including the president and local school district board members and everything in between at the same time.
What's more, elections are managed/run at the county level, not at the state or Federal levels. As such, there isn't just one election in the US on election day. Rather, there are 3500+ elections, each with different ballots, different folks managing the elections and different sets of interested parties monitoring each of those 3500+ elections.
While many offices are up for election every two or four or six years, not all of them fall on even-numbered years like the Federal elections.
My state has state elections that happen in concert with Federal elections, but my local government does not. In fact, we're voting for mayor, City Council and every other elective city office in a few weeks, even though the federal and state elections aren't this year.
Since elections are managed and run at the county level, there is little uniformity -- and less opportunity for widespread fraud.
When there are multiple simultaneous elections happening in the UK you get multiple ballot papers - one per race. You then put them into separate ballot boxes. This obviously doesn't scale elegantly to the kind of ballots that go from President to dog-catcher, but you could certainly separate them into pink, blue, yellow, and white ballots and count in parallel.
You don't have to use the same system for the higher risk ballots.
A foreign state isn't going to spend millions trying to subvert the vote for the head of "Wyoming School Board 45".
When I was at university our student elections were done on computer. 20 years ago. Nobody really cared about them, it was perfectly reasonable, you'd only have to bribe/threaten 3 people to make the result whatever you wanted.
If you put the national election in the hands of 3 people though, then you have a major problem.
They vote for everything including the president and local school district board members and everything in between at the same time.