German Finance Minister Wolfgang Schauble, evidently tired of getting phone calls from American officials urging Germany to restructure Greece's debts, says he trolled Treasury Secretary Jack Lew a bit about the ongoing debt crisis in Puerto Rico.

"I offered my friend Jack Lew these days that we could take Puerto Rico into the euro zone if the U.S. were willing to take Greece into the dollar union," Schauble said to Bloomberg. "He thought that was a joke."

Presumably Schauble was, in fact, joking, but it's worth saying this would be a terrible trade for the United States of America. Puerto Rico is both smaller than Greece (3.5 million people versus 11 million) and considerably richer ($23,678 GDP per capita versus just $18,863).

Nor are the debt situations remotely comparable.

Puerto Rico owes about $70 billion, giving it a debt-to-GDP ratio of nearly 70 percent, while Greece owes €323 billion, or about 172 percent of Greek GDP.

Last but by no means least, while Puerto Rico is in serious trouble from the standpoint of Puerto Rico, it is not by any means posing a threat to the stability of the United States of America or the dollar as a viable economic zone. Maybe the US Congress will let Puerto Rico default on its municipal debts, or maybe it will give bondholders an unrestricted right to try to immiserate the island. Either way, many Puerto Ricans will probably continue moving to the US mainland. And either way, those Puerto Ricans who do remain on the island will nonetheless be protected by Social Security, Medicare, Medicaid, the FDIC, and other US government programs.

Puerto Rico is, in other words, richer than Greece, better protected on the downside, and also less of a problem for the rest of the dollar area. So while this was a nice try by Schauble, the USA is better off standing pat.