"Spoiled" ballots (caused by voters doing something invalid) were systematically
manipulated, and both handled and encouraged in intentionally biased nonuniform ways,
to successfully hand the 2000 US presidential election to Bush and not Gore in
Florida 2000.
The problem of ballots "spoiled" by "accident" is
really hardly a problem at all (true accidents would tend to cancel out and lead to only
a very tiny
noise level) – the real problem is intentional manipulation
intended to create biases that do not cancel out.
Ballot spoilage is one of several important
biasing tools used by contemporary US election manipulators on a massive scale (others
include massively unequal voter registration and purging policies).
Uniform nationwide standards
for ballot "spoilage" and
voter registration should be adopted, instead of
allowing individual districts and counties and states
to make up their own each election, often on whim or (what is worse)
as directed by higher-ups.