Those bonds were issued to Social Security in the past in return for the Social Security surpluses over the years given to the federal government for its general spending programs, paying for everything from foreign aid to bridges to nowhere.
They were lent to the federal government and spent on other government programs, from foreign aid to bridges to nowhere, with the Social Security trust funds receiving only internal federal IOUs promising to pay the money back when it is needed to pay benefits.
Like his fellow Foreign Service officers, he built bridges across oceans and cultures, and was deeply invested in the international cooperation that the United Nations represents.