Pennsylvania voters will use 1980s machines, made by firms that no longer exist, that produce no paper record of their vote. What could go wrong?

When the United States goes to the polls on November 8, voters in Pennsylvania will be touching the lighted buttons on electronic vote counters that were once seen as the solution to messy paper ballots.

But in the event of a disputed election, this battleground state — one of the few that relies almost entirely on computerised voting, with no paper backup — could end up creating a far bigger mess.

Stored in a locked warehouse near downtown Harrisburg, the 1980s-era voting machines used by Dauphin County look like discarded washing machines lined up in rows. When unfolded and powered up, the gray metal boxes become a familiar-looking voting booth, complete with a curtain for privacy.

Much may rest on the reliability and security of these ageing machines after an unprecedentedly combative presidential campaign that is ending with Donald Trump warning repeatedly of a “rigged election” and his refusal at last Wednesday’s debate to commit to accepting the results.

The Republican presidential nominee has specifically targeted Pennsylvania as a state where the election may be “stolen,” despite no evidence to back up such a claim and several polls showing Democratic rival Hillary Clinton well ahead of him here.