There is no single national election in the United States in an administrative sense. Voting is organised by thousands of local jurisdictions, and that fragmentation is the deliberate result of how authority is allocated.
Authority runs downward from the states
The states hold the primary responsibility for the time, place and manner of elections, and federal rules set limits rather than running the process itself.
Most states in turn delegate the operational work to counties or, in some places, to municipalities, which handle registration, polling places, ballots and counting.
The result is that a federal contest is administered by a large number of independent offices, each answering to state law rather than to any national authority.
Ballots differ street by street
A ballot contains every contest a given voter is entitled to decide, and those contests include school boards, judgeships, local measures and district-level offices.
Because district boundaries cut across one another, a single county can require dozens or hundreds of distinct ballot versions for one election day.
Preparing, proofing and distributing those versions is a substantial administrative task, and it is a common source of the errors that surface on election day.
Equipment and procedure vary by jurisdiction
Counties purchase their own voting equipment within state certification rules, so neighbouring jurisdictions frequently use different systems with different failure modes.
Procedures for early voting, mail ballots, identification and the handling of provisional ballots also differ, since they are set by state law and interpreted locally.
Comparisons between places therefore require knowing which rules applied, because the same voter behaviour produces different recorded outcomes under different procedures.
Counting speed reflects rules, not diligence
Some states permit mail ballots to be processed before election day, while others prohibit any handling until the polls close, which changes when results become available.
Because different categories of ballot are counted in different orders, early returns can lean one way and later returns another without anything irregular occurring.
Certification follows days or weeks later, after reconciliation and any required audit, and it is that step rather than the reported count that makes a result official.
Local staffing is the binding constraint
Polling places are run largely by temporary workers recruited for the day, trained briefly and paid modestly, and recruitment is difficult in many jurisdictions.
Election offices themselves are small, often a handful of permanent staff managing a process that scales enormously for a few weeks every couple of years.
That mismatch between routine capacity and peak demand explains most of the operational strain visible on election day, more than any single decision made higher up.