Mark Cuban warned Elon Musk on X that Donald Trump is only loyal to himself.Christopher Willard/ABC via Getty Images; Alain Jocard/AFP via Getty ImagesElon Musk shared another post on social media expressing support for Donald Trump.Mark Cuban responded that Musk's loyalty to Trump won't be rewarded.Cuban wrote that Trump's "loyalty is only to himself."Mark Cuban warned Elon Musk about supporting Donald Trump in a social media post on Sunday, as the online feud between the two billionaires continues.Musk, who has endorsed the GOP nominee and set up a pro-Trump super PAC, reiterated his support for Trump in a post on X on Sunday morning, accusing the Democratic party of deliberately bringing immigrants into the US and key swing states to bolster support.