Mitt Romney said that Donald Trump's election could lead to what he called "trickle-down racism" spreading across the country.
"I don't want to see trickle-down racism" Romney said in an interview with CNN's Wolf Blitzer.
"Presidents have an impact on the nature of our nation, and trickle-down racism, trickle-down bigotry, trickle-down misogyny, all these things are extraordinarily dangerous to the heart and character of America," he added.
Click through images from Mitt Romney and Barack Obama during 2012 election:
Trump has come under fire for his racially charged attacks on US District Judge Gonzalo Curiel, who is presiding over a lawsuit against Trump's now defunct real-estate school, Trump University.
Several high-profile Republicans, including House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, have distanced themselves from the attacks, although they have publicly affirmed their support of the presumptive Republican presidential nominee.
The architects of the Republican national-security agenda have also pushed back against Trump's proposed barring of Muslims entering the US.
Romney has been the target of sharp criticism for comments he made during the 2012 presidential election. News outlet Mother Jones published secretly recorded video of Romney telling a group of donors that 47% of Americans would vote for Obama because they are "dependent on the government."
The 2012 Republican presidential nominee has been an outspoken critic of Trump, and attempted to recruit a third-party candidate to mount an independent run against the business mogul. Romney was floated as a possible candidate for the anti-Trump movement, although he ruled that out during the interview.
I think you're not going to find a credible candidate actually running as a third-party contender. The only way to win the White House, in my view, is to become a nominee of either the Republican or the Democrat Party, and simply running to be a spoiler would not give the American people I think the chance to express their own views about Mr. Trump or about Secretary Clinton.
Watch a segment from the interview below: