Trump opened a Saturday Pennsylvania rally with a vulgar riff on golf legend Arnold Palmer. It's the latest in what some see as a bizarre string of performances.

Donald Trump’s repeated gaffes, non sequiturs and unusual behavior have opened the door to questions from opponents about the 78-year-old Republican presidential nominee’s mental and physical fitness.

From bopping to the beat of his music playlist for nearly 40 minutes at a recent swing state town hall to his pro-Vladimir Putin blaming of Ukraine for Russia’s invasion, to criticizing former President Abraham Lincoln for not “settling” the Civil War, to riffing on locker room gossip about a pro golfer’s anatomy, Trump is providing plenty of fodder for rivals who’ve declared him “unhinged” and worse.

As Republicans did to 81-year-old President Joe Biden earlier this year, Democrats including horror novelist Stephen King and former presidents Bill Clinton and Barack Obama are seizing every opportunity to bash Trump − and it’s a target-rich environment.