I believe you are referring to the amount of income in which FICA deductions stop. Usually around September or October, I get a sudden boost in my take-home pay because my maximum FICA level was reached ($147K last year - $160K for 2023). It's nice to get that little bump in pay at the end of the year but raising that to your $400k is probably the most painless way to bring more money into the system.
But I would not support that until they (SSA) stop expanding the program in order to send checks to people that didn't earn them (like SSI). That is where we need to start first.
I would easily go with your last statement. Too many are on SSDI which I hear is from the general fund but I don’t trust them to say the truth (SS people).