The Supreme Court decision is just the latest to go against the president, who in a long tirade attacks the judges - many of whom he himself appointed.
"These are not the people I interviewed to sit on the Supreme Court, they are just a shell of their former selves, a court that is costing the United States trillions with its shockingly bad decisions," he writes on Truth Social.
Too close to the election
The Supreme Court's decision means states can continue to mail out ballots according to the procedures they have used for years. If Trump's new plan had been approved, critics say it could have resulted in millions of mail-in ballots not being sent, and Democrats have accused Trump of "virtually eliminating mail-in voting ahead of a key election."
Republicans, for their part, argue that the new decisions must be approved to curb what they see as widespread election fraud.
The judges do not completely oppose the Republican plan, but at least Trump-appointed Brett Kavanaugh believes that it cannot be implemented so soon before the November elections.
"Crazy Democrats"
Trump claims in his post that the US is the only country to approve postal votes, but according to AFP, the US currently uses similar rules to about 30 other countries. The fact that the Supreme Court is now going against him is, according to the president, because they are being intimidated by "crazy and depraved Democrats" and are not acting independently.
Earlier this summer, the Supreme Court rejected Trump's executive order to revoke birthright citizenship in the United States. The court has also ruled against him this year on issues of punitive tariffs.
