Although the unemployment certainly doesn't help things, it is not a cause of the existing Social Security problem. The existing Social Security problem we now have was recognized and predicted, universally and fairly accurately, 30 years ago, long before the current unemployment situation of the last three years. A stop-gap measure was passed to try to prop it up during either the Bush I or Clinton presidency, in one of those occasional exercises by Congress to try to appear to be responsible, again long before the current unemployment situation.
At some fundamental level it actually is that simplistic. We may not like the math, but the numbers don't change just because we don't like them.