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Democratic presidential candidate Bernie Sanders on Monday said Donald Trump’s remarks about Mexican immigrants are “an outrage” and “totally unacceptable,” but stopped short of calling the Republican a racist.

“For a major candidate for president of the United States to be throwing slurs at one group of people because of the country that they came from is totally unacceptable. Period,” Sanders told reporters after speaking at the National Council of La Raza’s Annual Conference.

The independent Vermont senator said the country should be proud of the progress it has made combating racial discrimination in recent decades, but that racism has been “a stain on human existence.”

When asked if he thought Trump is a racist, Sanders, who is polling second among Democrats challenging Hillary Clinton, said, “I don’t want to psycho analyze Donald trump what he said is an outrage.”

Trump defended his immigration views on Saturday during a rally in Phoenix, Arizona, that drew thousands of supporters.