According to Overton's 2006 book: In 33 out of 50 states, the election director (e.g. Secretary of State) is an elected partisan like Katherine Harris in Florida 2000. Plus in many other states that position is appointed by the governor, which almost ensures you get maximal partisan bias (if the governor is either Democrat or Republican, which is the case in year 2006 in 50 out of 50 states).
Famously, Katherine Harris served simultaneously as Florida's "unbiased" elections supervisor, and as the (maximally biased) Florida campaign co-chair for Bush in the 2000 USA presidential election. Gumbel notes on p.211 that Harris and FL Governor Jeb Bush (president Bush's brother) were in regular email contact during the [Bush-Gore 2000] recount. But we will never know what those emails said, because the operating system on Harris's office computers was hastily changed, erasing the messages. Intruigingly, the substitute OS was older than the one it replaced. J.Kenneth Blackwell did the same thing in Ohio in 2004 – but then took it to an even higher level by actually running for Ohio governor in 2006 while supervising his own election (with hire-and-fire power over every election official in the state). Connecticut's (elected Democratic) Secretary of State Susan Bysiewicz also tried to run for governor in 2006, at which point she also would have been supervising her own election if she stayed in office. However, when it became clear she would not win the Democratic Party primary, she dropped out of the race.
In contrast: many other countries use independent election officials or commissions: Australia, Brazil, Canada, India, Iraq, Mexico, Russia, S.Africa, and United Kingdom.
Others have oversight body composed mainly of judges: France, Germany, Spain, Argentina, Japan, New Zealand, Israel.