I think there are some inaccurate statements made regarding the Social Security Trust Fund and how it is invested in not only this parties platform but generally in the public.
It has to be invested and currently is invested in special issue bonds and shorter-term (less than a year) certificates. https://www.ssa.gov/cgi-bin/investheld.cgi
The aggregate interest rate is currently just above 3% annually. While the money is "spent" it is also paid back with interest. Federal debt level and deficit are also of great concern in the ability to pay back this debt.
In order to save social security, a program that I think is very necessary and has worked well, some changes need to occur in order to remain solvent.
Increase tax revenue coming in with a number of methods. An increase in minimum wage also increases the tax revenue as its a percent of wage, increase in the tax rate, increase the income cap on employee and/or employer taxable wages. increase the rate of return on investments by including State and Municipal Bond issues that are at a higher interest rate than current investments. These should be no lesser than AA+ or AA rated.
There have been a number of proposals over the years but little recent actions. https://www.ssa.gov/OACT/solvency/index.html
I believe this should be one of the main issues with all our elected officials at the Federal Level to take action.