Donald Trump has suggested November's presidential election be postponed, saying increased postal voting could lead to fraud and inaccurate results.
He floated a delay until people could "properly, securely and safely" vote.
There is little evidence to support Mr Trump's claims but he has long railed against mail-in voting which he has said would be susceptible to fraud.
US states want to make postal voting easier due to public health concerns over the coronavirus pandemic.
Under the US constitution, Mr Trump does not have the authority to postpone the election himself. Any delay would have to be approved by Congress. The president does not have direct power over the two houses of Congress.
In a series of tweets, Mr Trump said "universal mail-in voting" would make November's vote the "most inaccurate and fraudulent election in history" and a "great embarrassment to the USA".
He suggested - without providing evidence - that mail-in voting, as it is known in the US, would be susceptible to foreign interference.
"The [Democrats] talk of foreign influence in voting, but they know that Mail-In Voting is an easy way for foreign countries to enter the race," he said.
Mr Trump also said postal voting was "already proving to be a catastrophic disaster" in areas where it was being tried out.
