They could never control his mouth or his tweets.They could to some extent. The Constitution limits all of them and over 230 years of Federal government has created many layers of protection. No doubt the Cold War and the idea of a single madman launching our nukes put some limits on the office of the President.
Still, Trump is good at finding loopholes and he exploited each one to the maximum. The next year or two will see Congress reevaluating our Federal laws governing the President and Congress. I think good will come from this little bit of history.
I sure hope they do, the checks and balances weren’t what I thought they were.