Democrats in 23 states and the District of Columbia sued to block the order.
A special election will be held in the coming months, according to state law.
Graham Platner officially withdrew from the Maine Senate race on Friday.
It's the latest instance of the Republican president trying to exert White House influence over how U.S. elections are conducted.
The Supreme Court, in a 5-4 decision, upheld state laws that allow the counting of late-arriving mail-in ballots even if they were postmarked by Election Day.
Gov. Gavin Newsom is calling for a national "billionaires' tax" and suggests the U.S. government should own a stake in AI companies.