Story highlights Warren has not yet endorsed a candidate for the Democratic nomination

This isn't the first time the Democratic Senator has warned voters about Trump

Washington (CNN) Massachusetts Sen. Elizabeth Warren on Tuesday attacked Donald Trump's rise to become the presumptive Republican nominee, tweeting that the real estate mogul "built his campaign on racism, sexism and xenophobia."

Within hours of Trump winning Indiana's Republican primary -- and Ted Cruz dropping out of the GOP race -- Warren wrote that Trump "incites supporters to violence, praises Putin, and is 'Cool with being called an authoritarian.'"

Here's what else is real: @realDonaldTrump has built his campaign on racism, sexism, and xenophobia. — Elizabeth Warren (@elizabethforma) May 4, 2016

.@realDonaldTrump incites supporters to violence, praises Putin, and is "cool with being called an authoritarian." — Elizabeth Warren (@elizabethforma) May 4, 2016

"There's more enthusiasm for @realDonaldTrump among leaders of the KKK than leaders of the political party he now controls," Warren wrote on Twitter.

There's more enthusiasm for @realDonaldTrump among leaders of the KKK than leaders of the political party he now controls. — Elizabeth Warren (@elizabethforma) May 4, 2016

CNN has reached out to Trump's campaign for comment.

Read More