Donald Trump‘s sharing a stern warning with Elon Musk … implying he’s better off staying out of politics entirely than supporting Democrats in the upcoming midterms.

The President of the United States drew the line in the sand for his former advisor during a phone interview with NBC News … telling them he would bring the smackdown on EM if he supports Dems instead of Republicans that vote for Trump’s tax and spending bill.

DJT said, “He’ll have to pay very serious consequences if he does that.”

It’s just the latest threat in a back-and-forth between Trump and Musk … coming a few days after Elon blasted the prez for the spending bill he felt was filled with pork — claiming President Trump only won the reelection because of him.

Trump called BS on the claim … and, then the fighting devolved into a good old-fashioned X-spat — with Musk saying the administration won’t release the Epstein files because the president’s name is all over them — something that hasn’t been proven, BTW.

The president told the press his former friend has “lost his mind” … but he wouldn’t spend much time thinking about their feud — however, it sounds like the tech mogul’s still in the prez’s thoughts.