The risk of houses going underwater right now is very real and likely will be very difficult for people to manage

 Why?

Because of the Iran war and the Oil Crisis and the Food Crisis people cannot drive like they used to. So, the first things that go is vacations. So, this affects the Travel and vacation market including all restaurants in the U.S. This also will affect both food and gas and diesel prices as well as anything made with oil anywhere including the price of plastic which is also made from oil.

So, the first houses to go underwater likely would be in lower class urban areas along with remote houses far away from gas stations and stores. These likely would be most affected price wise. So, if these houses aren't paid off it becomes very problematic to hold onto them if the value of the house or building goes underwater (which means the real value of the house or building is less than the mortgage. This then means you cannot refinance the loans because you have no equity to borrow from. So, the likelihood of losing that home becomes greater and greater as the home loses value.

Then there is another factor: If people are losing their homes because they cannot refinance them around where your home or building is then the value of each of the remaining homes becomes less and less. this is a factor too. 

So, looking at what Trump is doing regarding everything right now it will destroy completely the middle Class and poor in relation to them all losing their homes from being underwater.

Then the rich like Trump scoop up those homes for pennies on the dollar from banks.

This happened during the Great Recession and also during the Great Depression too where the Rich make a killing on the suffering and death of the poorer people. 

So, this likely will just be a repeat of the Great Depression or Great Recession once again where Trump and his buddies make a fortune over time from the suffering of others.