Sen. Mark Kelly (D-Ariz.) slammed Donald Trump over a memo directing the Navy to remove the advanced system used to launch fighter jets from its newest aircraft carrier and to return to an older version, which officials say would be costly.

On Thursday, Trump ordered the U.S. Navy to remove the newer Electromagnetic Aircraft Launch System (EMALS) from aircraft carriers for launching fighter planes and revert to steam catapults, according to The Wall Street Journal.

“The Department of War shall restore both capacity and competition to the maritime industrial base as it expands our naval force structure,” Trump said in the memo.

”It will use proven, reliable and affordable technologies and ship designs, as well as award contracts that enable purchases from foreign suppliers in the near term while simultaneously incentivizing investment in America’s shipbuilding industrial base, consistent with other major equipment purchases such as icebreakers,” he continued.

Kelly, a former Navy combat pilot who sits on the Senate Armed Services Committee, said Trump should stick to what he knows best.

“I’ve launched off the front of aircraft carriers hundreds of times, have a Master’s degree in aeronautical engineering, and am a test pilot and even I wouldn’t suggest to the Navy how to engineer specific systems on its ships,” Kelly wrote in a post on Twitter.

“Donald Trump should stick to what he knows best — ballrooms, bankruptcy, and bullshit,” the senator added.

Kelly doubled down in an interview on MS NOW, calling Trump a “marginally failed real estate developer with multiple bankruptcies.”

“He shouldn’t be weighing in on systems, on aircraft carriers,” he said, adding, “Donald Trump knows nothing about this stuff.”

Kelly reiterated that even with his degree in aeronautical and marine engineering and his work as a test pilot, he would not tell the Navy how to change the systems on ships now.

“Not in any world would I suggest to the Navy to change the design of some system on a ship at this point,” he said. “I mean, does the guy know nothing about the way our government is supposed to work and how it’s supposed to be managed?”