Elon Musk’s war on MAGA has quickly gone nuclear after the billionaire CEO blasted a social media user’s comments about H1B visas Friday, and former Trump chief strategist Steve Bannon called him a “toddler” for his response.

Donald Trump has backed Elon Musk in supporting visas for skilled migrants. The president-elect waded into a row that has split the Republican party by defending H1B visas, which permit highly-educated foreigners to work in the US for up to six years.

Less than a month before Donald Trump returns to office, two of his most ardent allies have plunged into a fierce online debate over immigration, specifically the government’s visa program that allows American companies to hire so-called “highly skilled” foreign workers.