President Barack Obama on Tuesday downplayed Donald Trump's suggestion that November's election is "rigged," and said the GOP presidential nominee needs to toughen up.

"I'd advise Mr. Trump to stop whining and try to go make his case to get votes," Obama said at a White House news conference alongside Italian Prime Minister Matteo Renzi.

"If whenever things are going badly for you, you start blaming somebody else, then you don't have what it takes to be in this job," Obama continued. "There are a lot of time things don't go our way or my way … that's OK, you fight through it."

Trump tweeted Monday about the "rigged system" that will impact the polls, although he gave no specific evidence for how results could be tainted. He also suggested that people who are dead are still able to vote and that undocumented immigrants will cast ballots.

Voter fraud, he added, is "very, very common."

Obama on Tuesday said he would reserve more scathing remarks against Trump for the campaign trail, but insisted that American elections can't be rigged because the process for voting for president is "so decentralized."

"One way of weakening America is if you start betraying those basic American traditions that have been bipartisan and have helped hold together this democracy for well over two centuries," Obama added.