The presumptive Republican presidential nominee tells The Wall Street Journal that US District Judge Gonzalo Curiel has "an inherent conflict of interest" because Trump is "building a wall," a reference to Trump's proposal to build a wall along the border between the US and Mexico.
Trump has brought up Curiel's ethnicity several times this year, including last week at a rally in San Diego.
Curiel was born in Indiana and served as a federal prosecutor and a judge in the California state judicial system before being nominated to the federal bench by President Barack Obama in 2011.