Extra care will need to be taken amid the added challenge of COVID-19 to "ensure that everyone's vote counts," said Ellen Weintraub.
Running a vote-by-mail election is surprisingly complicated and there's a "leaky" pipeline for mail-in votes in many states, experts have warned.
Mail delays bedevil the Postal Service amid a pandemic and with November's election set to see record numbers voting by mail.
The president tweeted that his first debate with Democrat Joe Biden should be earlier than the current schedule, which starts Sept. 29.
The ruling overturned an earlier expansion for absentee ballots after some voters sued, saying they were concerned about the pandemic.
The North Dakota Republican also suggested COVID-19 death counts may be inflated.
President Donald Trump’s campaign adviser Mercedes Schlapp was called out on CNN after she falsely claimed mail-in voting leads to voter fraud.
The MSNBC host said the president is leading a "full, concerted effort ... to undermine the legitimacy of the election."
CNN's Brianna Keilar repeatedly fact checked Mercedes Schlapp's apparent attempts to villainize mail-in voting.
"I think we've actually had success with mail-in voting in my state. I've voted remotely before and I haven't had any challenges," Sen. Todd Young said.