"I continue to believe Mr. Trump will not be president," Obama said on Tuesday at a news conference in Rancho Mirage, California after a meeting with southeast Asian leaders.
"And the reason is that I have a lot of faith in the American people. Being president is a serious job. It's not hosting a talk show, or a reality show," he added.
Trump is the frontrunner in the race to be the Republican Party’s nominee for president. The billionaire businessman has already won the New Hampshire primary, and leads the polls in South Carolina, where Republicans are scheduled to vote on Saturday.
US President Obama: Trump Will Never Be Elected US President
When Obama was asked by a reporter about Trump at the Association of Southeast Asian Nations (ASEAN) summit, the US president said the American electorate will never pick him because "they recognize that being president is a serious job.”
The presidency isn't "a matter of pandering and doing whatever will get you in the news on a given day. And sometimes, it requires you making hard decisions even when people don't like it," Obama said.
In response, Trump called Obama "the worst president in US history."
"Interesting how President Obama so haltingly said I 'would never be president' - This from perhaps the worst president in US history," Trump tweeted on Wednesday.
Trump also responded to Obama during an event on Tuesday evening in Beaufort, South Carolina, saying it was “a great compliment” to be censured by a president who had done so much damage to the country.
"He has done such a lousy job as president," Trump asserted, adding, "You're lucky I didn't run last time when Romney ran because you would have been a one-term president.”
Trump, who has never held elected office, is still leading the Republican presidential primary field, despite the fact that his campaign has been marked by controversial statements, including with disparaging remarks about Mexican immigrants, women and Muslims.
Trump says he would deport 11 million undocumented workers from the United States and would establish a "deportation force" for this purpose.
He has also promised to expel undocumented immigrants and build a wall on the US-Mexico border. In addition, he has proposed repealing the constitutional right to citizenship of anyone born on US soil.
Trump has also created a furor in the US and around the world by proposing a "total and complete shutdown of Muslims" entering the United States, following a mass shooting in California.
The New York real-estate mogul has also called for a database to track Muslims across the United States, and he has also said that the US would have "absolutely no choice" but to close down mosques, AFP reported.
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