The tweet came as a surprise, even from the provocative Donald Trump: "I HATE TAYLOR SWIFT!" the former president said Sunday.
Though the all-caps post came without accompanying commentary or explanation, the context was clear.
On Tuesday, just minutes after a debate with Vice President Kamala Harris that Republican Trump was widely seen as losing, the superstar singer/songwriter posted a message on Instagram saying she would vote for his Democratic rival, calling Harris a "steady-handed, gifted leader."
Celebrity endorsements rarely carry enormous weight, but the hugely popular Swift is seen as being in a class of her own, with more than 100 million followers on social media - 10 million of whom "liked" her Instagram post.
"Going after Taylor Swift is a genuinely bad campaign strategy," said one poster on social media platform X.
“Taylor doesn't get mad, she gets even.”
It was unclear what Trump hoped to gain by attacking Swift, though he may calculate that any publicity is better than none.
He has been criticised, even by fellow Republicans, for his recent association with conspiracy-minded right-wing influencer Laura Loomer, who has at times joined him on his campaign plane.
The 31-year-old Loomer - who has called the Sept. 11 terror attacks an "inside job" and said some recent mass shootings were staged by Democrats - recently suggested that Swift had entered an "arranged relationship" with football star Travis Kelce "to influence the 2024 election."
There is no evidence to support any of those claims.
AFP