The crumbling "bricks" that make up the rest of the wall are the voters who support him.  It's criminal that if you take away the racists, misogynists and the too stupid to breath if they had to think to do it you're left with a core of economically destroyed people harboring legitimate anger but who can't bring themselves to blame Republicans for creating a political imperative that "greed is good".  At the same time they only see the DINOs' in the Democratic Party who either ignored them or voted with Republicans to screw them.
Even when Obama had a first term mandate and a Democratic Congress he failed to break the power of Wall Street, failed to break up too big to fail banks, failed to kill corporate controlled trade agreements under negotiation and squandered his power on the ACA in which he failed to demand single payer instead invited Republicans and health insurance companies to help write the reform bill.
Trumps' popularity is no surprise, just very disappointing.