As of Sunday morning, the hashtag was the second highest trending on Twitter, with more than 77,600 tweets, including a journalist and an NAACP leader.
"Dear Grim Reaper, You took the #wrongtrump," tweeted Bishop Talbert Swan, who is a pastor, radio host, and president of the Springfield, Mass., branch of the NAACP.
"What did he promise the devil for the Grim Reaper to take the #wrongtrump ???" tweeted journalist David Leavitt.
A number of the posts bearing the hashtag were expressing distaste for the trend, even by some who oppose the president.
"I dislike trump with my whole heart & he will never get my vote but the #wrongtrump hashtag makes me so uncomfortable as a human being with a heart and compassion for life," said mental health advocate Kenidra Wood.
Robert Trump died Saturday, 11 days before what would have been his 72nd birthday. President Trump had traveled to New York on Friday to visit him. Robert had reportedly spent more than a week in the intensive care unit at Mount Sinai Hospital in New York City earlier this summer.
"It is with heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight," the president said in a statement. "He was not just my brother, he was my best friend. He will be greatly missed, but we will meet again. His memory will live on in my heart forever. Robert, I love you. Rest in peace."
Fox News' Morgan Phillips contributed to this report.