Why is the midterm vote count taking so long in some US states?

In the House there are still more than 40 seats yet to be called, with at least a dozen of them highly competitive.

So what is it about the US electoral system that makes counting votes apparently so tortuously slow?

Responsibility for running fair and fast elections, like much of the way the country is governed, is devolved to each of the 50 states. How the count is done, and its speed, varies slightly between each state. (Election deniers have tried to imply that slow counts are somehow irregular or fraudulent. They are not.)

In this cycle, much of the heat is engulfing just three states: Arizona, Nevada and Georgia.

Several of the most consequential races are happening in the border state of Arizona. A US Senate contest between the Democratic incumbent Mark Kelly and Republican challenger Blake Masters could determine which party controls the Senate.

There are also consequential state races, including for governor and secretary of state, in which prominent election deniers endorsed by Donald Trump have a shot at winning. So far only 70% of the Arizona vote has been counted.

To understand why that is, you have to zoom in to Maricopa county, which covers the state capital, Phoenix. It contains 60% of all votes in Arizona and is the second largest voting jurisdiction in the nation.

But the main reason why Ron DeSantis won his re-election race so quickly on Tuesday was because it was a blowout, with the incumbent Republican governor garnering 59% of the vote while his challenger, Charlie Crist, received only 40%.

Had the candidates we are watching in Arizona or elsewhere had such a convincing lead, we would probably not still be waiting for their races to be called. Nonetheless, there are questions that Arizona is going to have to face in future elections.

Nevada is going a bit faster than Arizona, with 83% of the votes counted, but this year the count could last through Sunday. But like in Phoenix, there are still large numbers of ballots yet to be processed in the big urban areas of Las Vegas and Reno.

There is a debate to be had about the merits of such a system. Many election officials stress that it is more important to have a system that is convenient, accurate and accessible than one that is fast.

The count in Nevada also has a lot riding on it. That includes a very close race between the sitting US senator Catherine Cortez Masto and Republican challenger Adam Laxalt; three tight contests for US House seats; and a battle involving one of the most visceral election deniers, Jim Marchant, who is running for the job of top election official.