Since 1978, first-term presidents held ceremonies in the East Room to unveil the portraits of their immediate predecessors. Trump, who long accused the Obama administration of illegally spying, broke the four-decade-long tradition and refused to unveil Obama’s presidential portrait. Reports said that the Obama family also had little interest in attending any such event.

NBC News – White House portrait ceremony may be the latest casualty of the political divide
USA Today – Report: Trump won’t unveil Obama’s official White House portrait anytime soon
Business Insider – Trump is refusing to unveil Obama’s portrait at the White House, breaking a 40-year tradition