REUTERS/Carlos Barria
President Barack Obama speaks during a joint news conference with Italian Prime Minister Matteo Renzi in the Rose Garden of the White House in Washington, U.S., October 18, 2016.
Obama also slammed Republicans who had previously been "anti-Russia" for embracing Trump's positions.
"Mr. Trump's continued flattery of Mr. Putin, and the degree to which he appears to model many of his policies and approaches to
"So you'll have to explain to me how it is that some of the same leaders of the Republican Party who were constantly haranguing us for even talking to the Russians and who consistently took the most hawkish approaches to Russia, including Mr. Trump's selection for vice president, now reconcile their endorsement of Mr. Trump with their previous views," he continued.
The Republican presidential nominee said Monday that it would be "wonderful" if he and Russian President Vladimir Putin could meet if Trump wins the election in November.
Trump and Putin have been broadly complimentary of each other as Trump has been running for president.
"If he says great things about me, I'm going to say great things about him," Trump said in September. "I've already said he is very much of a leader. The man has very strong control over his country."
Trump has also said that it would be "great" if the US could "get along" with Russia. But Obama cautioned against being too warm toward the country.
"We think that Russia is a large, important country with a military that is second only to ours and has to be a part of the solution on the world stage rather than part of the problem," he said. "But their behavior has undermined international norms and international rules in ways we have to call them out on."