With the coronavirus pandemic raging across the United States, mail-in voting is expected to surge as voters shy away from attending polling booths in-person.
President Donald Trump, without evidence, has slammed the practice as fraudulent and accused opposition Democrats of working to use it to rig the 3 November election.
“The only way they can take this election away from us is if this is a rigged election,” Mr Trump said on Monday night during the Republican National Convention.
Democrats and unions have accused Mr Trump of taking the service “hostage” to make it harder to vote by mail.
But how has a seemingly innocent practice become such a divisive issue in the US?
How many Americans will vote by post?
Despite Mr Trump labelling mail-in voting a risky and unproven practice, it has actually been used in the US for more than 150 years.
In the American Civil War, Republican President Abraham Lincoln allowed Union soldiers on the battlefield to vote through the mail. Notably, only troops in Republican-governed states participated, with Democrats fearing the scheme could help their opponents.
Since then, mail-in voting has become a feature of the US democratic system, with an increasing number of electors shunning voting booths on polling day.
In the 2016 presidential election, two in five voters voted early, with around six per cent voting by mail.
In 16 states, more than half of voters cast a ballot early, with Arizona, eventually won by Mr Trump, recording the highest rate of early voting at 75 per cent.
Because of COVID-19, the number of people opting to vote by mail in 2020 is expected to more than double, with at least three quarters of all Americans eligible to vote through the mail, according to the
Nine states, as well as the District of Columbia, are planning to expand access to postal voting by holding 'all-mail' ballots.
Under this model, every elector is sent a ballot to be returned by election day – similar to the way Australia held its postal plebiscite on same sex marriage in 2017.
Protesters in Washington DC protest outside the home of USPS Postmaster General Louis DeJoy Source: Michael Brochstein/Sipa USA
Why has the post office become a political issue now?
The government-owned United States Postal Service (USPS) - which runs at a loss, but keeps vital mail routes open to people across the country - has become a political flashpoint in recent months.
Mr Trump, who is trailing Joe Biden in the polls, has been opposing new postal funding because of his opposition to mail-in voting and unsubstantiated claims it is rife with fraud.
In 2018, a now-disbanded voter fraud commission launched by the Trump administration uncovered no evidence to support claims of widespread voter fraud.
In fact, university found only roughly 1,200 cases of voter fraud over the past 20 years across all elections in the US.
“That is just one case per state every six or seven years - we are talking about an occurrence that translates to about 0.00006 per cent of total votes cast,” the study’s authors .
In May, the House of Representatives passed a $3 trillion (USD) coronavirus relief package, which included additional money to assist the USPS and funding to expand postal voting.
But the bill remains stalled in the Republican-controlled Senate.
Experts say the popularity of postal voting in the US differs among Democrats and Republicans.
“[While] mail-in voting encourages people to actually engage in the democratic process ... it tends to favour Democrats, whereas Republican voters can be much more engaged to attend polling booths on election day,” Swinburne politics lecturer Bryan Cranston said.
Postmaster controversy
In June, Mr Trump appointed Republican donor Louis DeJoy as the new US Postmaster General.
Mr DeJoy has already presided over the removal of mail collection boxes and processing equipment, and overseen a cut in overtime pay.
"These changes, creating our new on-time transportation network and designing an engaged functional organisational structure, will be the catalyst for the significant improvements in cost, performance and growth," Mr DeJoy told the House of Representatives Oversight Committee on Monday.
Mr Cranston said the changes could have a big impact on the election.
“If there is a delay in the delivery of that mail, potentially, you could have a lot of votes that aren't actually received by the close of the polls,” he said.
“There is a big question at the moment about whether this is election interference or not, but it would suggest these measures are being done in order to limit the opportunity for many people actually engaged in the voting process.”
The USPS has warned most states that it cannot guarantee on-time delivery of mail-in ballots.
Following a huge public outcry, it was announced last week that it would hold off on the cost-cutting operational changes until after the election.
How common is mail-in voting elsewhere?
Mail-in voting is common in most other Western democracies, including Australia.
At last year's federal election, 8.27 per cent of voters mailed their ballots before polling day on 18 May, with Queensland recording the highest percentage of postal voting.
Other recent polls have also seen an uptick in mail-in ballots, with Australians advised against gathering in large numbers due to COVID-19.
A record 560,000 postal vote applications were sent in for Queensland’s local government elections in late March - almost 17 per cent of all enrolled voters.
The closely contested Eden Monaro federal by-election in July also saw a rise in postal voting, with more than 13 per cent of all votes mailed before polling day.
The trend is likely to be replicated during state and territory elections - the Northern Territory Electoral Commission reported 53 per cent of voters had already voted before last Saturday's election.
Queensland, the ACT and Western Australia are all holding state or territory elections in the next 12 months.
