"Nikki Haley voters, Donald Trump doesn't want your vote," Biden said in a social media post on Friday that included a link to a new ad from his campaign. "I want to be clear: There is a place for you in my campaign."
The ad shows video clips of Trump blasting Haley as "birdbrain" and dismissing her candidacy.
"She's gone crazy, she's a very angry person," Trump said in one video clip of his former U.S. Ambassador to the United Nations.
Representatives for Haley and for Trump did not immediately respond to requests for comment.
Haley stuck with her presidential race when other Trump challengers had dropped out, promising policies that appealed to Republicans who had rejected Trump.
Almost 570,000 voters in three key battleground states - Nevada, North Carolina, and Michigan - voted for Haley in the Republican nominating contest, a small but potentially significant group in races that have been decided by tiny margins in recent elections.
Many Haley voters have wondered if they still have a place in the Republican Party, which has coalesced around Trump, despite his repeated lies about having won the 2020 election against Biden, and the Jan. 6, 2021, riot at the U.S. Capitol.
Biden, 81, will need as much support as he can muster. He has faced concerns about his age and fitness for a second four-year term. Recent Reuters/Ipsos polls show his approval rating at 40% and in a tight race with Trump, 77, ahead of the Nov. 5 election.
(Reporting by Steve Holland and Tim Reid; Editing by Heather Timmons and Bill Berkrot)
