Why are Mortgage Rates Increasing?

Investopedia quote, "When the Fed makes it more expensive for banks to borrow by targeting a higher federal funds rate, the banks in turn pass on the higher costs to their customers. Interest rates on consumer borrowing, including mortgage rates, tend to go up."

https://www.investopedia.com/articles/personal-finance/050715/how-federal-reserve-affects-mortgage-rates

Overlay the Fed Funds Rate ( https://fred.stlouisfed.org/series/FEDFUNDS ) with the Federal Debt ( https://fred.stlouisfed.org/series/GFDEBTN ) level since 1980. A perfect inverse correlation. As the debt goes up over time the rate goes down over time. 

The Federal government has reached a record debt level ($30 Trillion), so if rates get raised it costs the government more in interest payments. They can not afford to service the debt with higher rates and would then default, which they have never done and must avoid at whatever cost. If the U.S. defaulted then status as world reserve currency would be over. 

Do you think rates can sustain at the current levels today? If so, for how long?