I'm thinking his willful failure to be briefed by the CIA about Russian election tampering and not understanding diplomatic protocall.
Making off handed statements without proper research about the mater.
I doubt this rises to the level of "high crimes and misdemeanors" constituting grounds for impeachment. It takes more than boorish behavior to be given the boot. He also has an anti-impeachment insurance policy: Pence.
I think it's more likely he will be frustrated and ineffective, having alienated all the Democrats and many influential Republicans in Congress. Pointing a finger and saying "You're Fired!" isn't the way it works in the halls of government.