He tried to, but his advisors stopped him. Bob Woodward reported that Gary Cohn snatched papers off his desk on multiple different occasions to stop him from starting trade wars at the beginning of his first term.

This time around he has made sure there are no advisors strong enough to stop him. That means he is far more dangerous now than he was in the first term. And not just in the area of the economy.

Also, he was concerned about getting re-elected again.

And possibly being prosecuted for crimes, but Republican appointees on the Supreme Court kinda took care of that.

There were adults in the room in the first term. Now, just loyalists, sycophants, and grifters.