As Bernie Sandersoutraises his fellow 2020 presidential hopefuls and pulls no punches in his criticism of the current administration, President Donald Trump has been taking to Twitter to rant against the senator from Vermont.

Trump tweeted about “Crazy Bernie Sanders” four times in less than 12 hours from Monday to Tuesday. The tweetbomb prompted observers to wonder whether Sanders was getting under the president’s skin ― a notion later floated by the senator himself.

In one tweet, Trump predicted that Sanders and “Sleepy Joe Biden” would be the top contenders for the Democratic nomination for president in 2020.

“I look forward to facing whoever it may be. May God Rest Their Soul!” Trump declared, without explaining his use of the apparently morbid phrase.

Trump also took aim at Sanders’ income as well as the senator’s Monday interview on Fox News, in which Sanders lambasted the president as a “pathological liar.”

Trump said it was “weird” to watch Sanders on his preferred news network and suggested, without evidence, that Fox News had prevented Trump supporters from entering the studio.