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Politicians hindering efforts to support Social Security had better hope they never get cornered by those who rely on those checks for their only income—because that amounts to 40.2 percent of seniors.

So says a report from the National Institute on Retirement Security, "Examining the Nest Egg: The Sources of Retirement Income for Older America," which points out that although in 2013 pensions did keep nearly a million retirees out of poverty while cutting the cost of public assistance by $4 billion, Social Security did far more—it kept more than 7.5 million households out of poverty and cut public assistance costs by $10 billion the same year.

Of course there are far fewer pensions in 2020 than there were in 2013. And, says the report, just 6.8 percent of American seniors get the "ideal situation" in retirement—income from Social Security, a defined benefit pension and a defined contribution account—to ensure retirement security.