"This is not entertainment, this is not a reality show. This is a contest for the presidency of the US," Obama said.
"With respect to the Republican process and Mr Trump, there's going to be plenty of time to talk about his positions on various issues. He has a long record that needs to be examined. And I think it's important for us to take seriously the statements he's made in the past," Obama told reporters.
This was Obama's first comment on Trump, who has courted controversies on several matters including on migrant issue and inconsistent foreign policy stance, after the outspoken real-estate mogul became the presumptive nominee last week.
Trump has provoked number of protests with his controversial speeches and proposals ranging from banning Muslims from entering the US to building a wall to keep out Mexican migrants to slashing US funding for NATO.
"I think I just want to emphasize the degree to which we are in serious times and this is a really serious job," Obama said and added that every candidate, every nominee needs to be subject to exacting standards and genuine scrutiny.
"It means that you've got to make sure that their budgets add up. It means that if they say they've got an answer to a problem that it is actually plausible and that they have details for how it would work, and if it's completely implausible and would not work, that needs to be reported on and the American people need to know that," he said.
"If they take a position on international issues that could threaten war or has the potential of upending our critical relationships with other countries or would potentially break the financial system, that needs to be reported on," Obama said.
"But what I'm concerned about is the degree to which reporting and information starts emphasizing the spectacle and the circus. Because - that's not something we can afford."
During the news conference, Obama also took a dig at the Republican leadership that has resulted in the rise of Trump.
"There is no doubt that there is a debate that's taking place inside the Republican Party about who they are and what they represent. Their standard bearer at the moment is Donald Trump," he said.
"Not just Republican officials, but more importantly, Republican voters are going to have to make a decision as to whether this is the guy who speaks for them and represents their values," Obama said.
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