Since the 80's, That process has been undercut by congress "loaning" then money to itself in the form of special bonds, and then using the proceeds to offset spending (such as excessive defense spending, welfare, and reducing taxes on the wealthiest 1% of Americans).
Check out the 1967 amendment to the Social Security Act. Just two years in, The Great Society already busted budget projections and, combined with LBJ's escalation in Vietnam, the budget deficit was getting out of control. Rather than admit they screwed up, Congress and LBJ agreed to amend the SSA to state that any government body program ran a surplus would transfer that surplus to the General Fund in return for the General Fund covering any deficits those programs ran in future years.
They knew the budget was unsustainable but they played accounting games to cover it up so they wouldn't have to be accountable to the people, which meant they could keep their jobs despite having pushed an agenda they knew would eventually bankrupt us. By the time the shit hit the fan, they'd be retired or dead - essentially untouchable. Earlier in that decade, there was a politician that would later become President who was already warning that Social Security was going to go bankrupt on its own, but I'm guessing that's the guy that gets most of the blame today, despite him not being the one that actually caused the problems or drained the Social Security Trust Fund (in fact, it wasn't even his party that created Social Security, The Great Society, the 1967 Social Security Amendment or escalated Vietnam, but most people blame them anyway because, ahem, "reality" has a well known liberal bias).