Breaking his 36-hour silence after prematurely declaring victory on Wednesday, the president continued spewing unfounded conspiracy theories about election fraud and illegal ballot-counting as he addressed Americans from the White House.
Once again, he claimed he had won the election, even as ballot counts continue.
Ms Power, the nation’s envoy to the UN during the second Obama administration, tweeted: “He’s going full Robert Mugabe”, referencing the Zimbabwean ruler’s grip on power for so many years.
Mr Mugabe ruled the southern African nation as its second president from 1987 to 2017, having also served seven years as the country’s first prime minister.
He was a controversial figure, hailed by some as a hero for his struggle against colonialism and white minority rule, and by others as a dictator responsible for corruption, economic mismanagement, and human rights abuses.
While opposition to Mr Mugabe grew in the 2000s, he was re-elected in 2002, 2008, and 2013, in campaigns noted for electoral fraud, nationalism, and violence.
He was eventually ousted in a coup by his own party in 2017, and died last year.
Some on Twitter disagreed with the characterisation, suggesting that he was in fact “going full Donald Trump”, that he was being “thoroughly American”.