For much of our history, the sheer difficulty of getting to America and surviving here ensured the nation was stocked with immigrants who represented a sort of natural elite.
No, these immigrants did not come from foreign aristocracies, nor need they come from any particular location, ethnic group or profession.
But before Franklin Roosevelt began establishing an American welfare state, and before a series of Roosevelt's successors decided they would make no serious effort to secure our national borders, immigrants to America had at least two things in common: The ability to get to a place that was hard to reach and the ability to survive there on their own.
Now America is becoming a magnet for high-school dropouts.
That is why the report that the Congressional Budget Office produced this month for House Budget Chairman Paul Ryan ought to become a focus of national debate, as members of both parties in Congress work with President Obama to try to give foreign nationals living here illegally a way to become citizens.
Here are some key facts presented by the CBO: 1) There are now 40 million foreign-born people living in the United States, making immigrants a bigger share of our national population than at any time since 1920. 2) Twenty-two million -- a majority of the foreign born -- are non-citizens. 3) Eleven-and-a-half million -- a majority of the non-citizens -- are illegal aliens.
A large majority of the illegal aliens in the United States -- 6.8 million, or more than 59 percent -- come from Mexico. About another 1.6 million -- or 3.9 percent -- are from El Salvador, Guatemala and Honduras.
How does the educational attainment of the foreign-born population in the United States compare to the educational attainment of the native-born population? It depends on where the foreign-born were born -- and what type of educational degree is in question.
Immigrants from Mexico and Central America are far less likely to have high school degrees than native-born Americans, while immigrants from Asia, Europe and Canada are more likely than native-born Americans to have college degrees.
"In 2012," said CBO, "27 percent of the foreign-born population between the ages of 25 and 64 had not completed high school, compared with 7 percent of the native-born population. More than half of the people from Mexico and Central America, 54 percent, had not finished high school, but only about 9 percent of the people from Asia and 5 percent of the people from Europe and Canada had less than a high school education."