(CNN) -- President Barack Obama sharply disputed Donald Trump's claim that the US election system is rigged, saying the Republican presidential nominee should "stop whining."
"He started whining before the game's even over," Obama said Tuesday during a news conference in the White House Rose Garden, adding that Trump's claim is "not based on facts."
Trump and his surrogates have in recent days claimed that the US election system is "rigged," coming after the candidate's two lackluster debate performances and a drop in poll numbers nationally and in key swing states.
Trump's preemptive warnings of a "rigged election" are entirely unprecedented in modern American political history, Obama said.
"I have never seen in my lifetime or in modern political history any presidential candidate trying to discredit the elections and the election process before votes have even taken place. It's unprecedented," Obama said alongside Italian Prime Minister Matteo Renzi.
He cast Trump's warnings as a debunked myth, saying no evidence of widespread voter fraud exists.
"If whenever things are going badly for you and you lose, you start blaming somebody else, then you don't have what it takes to be in this job," Obama said.
Obama also said Trump's "flattery" of Russian President Vladimir Putin is "out of step" with US norms.
"The degree to which he seems to model many of his policies and approaches to politics on Mr. Putin is unprecedented in American politics and is out of step" with bipartisan approaches toward Moscow, Obama said.
Obama said Trump's actions rarely surprise him anymore. But he said he was bothered by Republicans who have traditionally taken a harsh stance on Russia, who now back Trump.