Trump does stuff not because he thinks pragmatically, but it is all about embracing the alt right base that so passionately support him.
Where the hell does Tucker Carlson get all his facts from? The actual fact is because the security situation in South Africa is of huge concern generally. As farms are the most vulnerable, they are targeted and have been for decades. As 8% of Whites own 72% of the farmlands, that is why the according to Tucker Carlson the "Whites" are targeted. The fact is that there are Blacks also who have been attacked and killed. But generally, in South Africa the number of Blacks being murdered are a huge percentage. Read some facts about the people who had no problems killing Blacks in South Africa and are still "proud" about it:
https://www.theguardian.com/guardianweekly/story/0,,1840575,00.html
Off course Tucker Carlson, Trump and the rest of the alt right wingers will never mention this fact.