Last night, former New Mexico Governor Gary Johnson finally squeezed into a major GOP debate and pulled off the best joke of the evening: “My next-door neighbor’s two dogs have created more shovel-ready jobs than this current administration.”

Laughs and levity all around. However, on Morning Joe today, Willie Geist passed on the news that hours before the debate, Rush Limbaugh had burst forth with: “My dogs have created more shovel-ready work than Obama has just this week alone.”

Uh-oh on Johnson. The Joe crew hinted that either a writer had handed Johnson the laugh line (which he, indeed, seemed to be reading), or that he had actually plagiarized Rush. Why would anyone be so stupid as to steal from the big man? they wondered. John Heilemann made a squinchy face at the very thought.

As it turns out, Johnson told the Huffington Post after the debate that he knew nothing of Rush’s knee-slapper and that he drew the line from “eight one-liners” that a former Tonight Show writer and Albuquerque radio host had texted him yesterday afternoon.

Rush, of course, claimed all the credit, telling Michael Calderone, “I guess I’ve become show prep for the GOP debates now, too.” (Not clear what achievements “too” refers to.)

But here’s the big scoop: It might have been Rush who either “plagiarized” or unknowingly regifted the joke: a real live dog originated the line two years ago! A Talking Points Memo slideshow of the Top Ten Protest Signs of 2009 included one photo of a black pooch in a red vest emblazoned with the words “I Create Two Shovel-Ready Projects/Day.”

Unless the dog stole the line from, say, an elephant.