It is legal.
I’ve asked multiple DOT officers (we’ve built structures for several).
You must be properly licensed, tagged, insured, secured, and you must have tires that are rated for the amount of weight you are carrying.
I’m sure some of that varies from state to state.
The tires on that rig would allow me to be nearly 58,000 lbs gross. I am allowed 7,000 lbs on the steer axle, 12,000 lbs on the drive axle, and 34,000 lbs on the trailer axles. Do the math on that, 53,000 lbs.
Would I do that? No, because I’m not tagged for that, and I couldn’t get 34,000 lbs on the trailer without over loading the drive, and I would be nervous about effectively stopping that weight. Mid 40,000 lbs is bad enough.