Former Housing and Urban Development Secretary Julián Castro said President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE’s electoral strategy is dividing Americans along racial lines, blasting him as an “identity politician” in an interview with NPR Tuesday.

"What he's trying to do is, he's trying to split people along racial and ethnic and religious lines," Castro told the "NPR Politics Podcast" and New Hampshire Public Radio. "His specialty, if you will, is division, trying to just amp up a base. He's the biggest identity politician that we've had over the past 50 years."

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Castro told the outlets that it was not enough to simply condemn Trump or his tweets as racist, saying it was also necessary to “counterprogram” him.

"How do you combat that effectively? Well, you do that in part by building coalitions," Castro said.

"And that coalition is going to be built of people of different backgrounds, different skin colors, different religions from throughout the country, that actually believe that we're a nation that will be more prosperous, more successful if we appreciate our differences,” he added.

The presidential candidate said Trump was making a risky bet by assuming that appealing exclusively to his base could secure another electoral college victory.

“The percentage of people, of voters, who agree with me I believe, is bigger than the percentage of people who agree with [Trump],” he said.

Castro, who has sparred with other Democratic candidates on his proposal to decriminalize crossing the U.S. border illegally, also told NPR that reducing the recent influx of migrants from Guatemala, Honduras and El Salvador would require increased aid to those nations.

"I think that we're always going to have people coming from Central America and other parts of the world," he said. "Do we need 140,000 people in one month coming from those countries? That's an indication that something is wrong in those countries and I want to help heal that."