He's letting the GOP, which controls congress, mostly get what they want, so it wouldn't make any sense to cut him off. In addition his popularity among their base is still quite high, so again, why cut him off.

(Nothing in the above statement above should be taken to imply that I oppose or support any member of the legislative or executive branches.)

Congress likes to be able to abdicate their responsibility and just pass it on to the president.

Realistically, if Trump truly had unlimited, unchecked power, immigrant slave labor would be building The Wall across the Mexican border as we speak.

You're right, but Congress has been essentially deadlocked into a completely nonfunctional body for years now. On top of that, the republicans necessary to curb trumps power are extremely afraid of his appeal in their base, that they'll lose their seats due to not being either on his side, or being enough like him.