Only 43 days after abandoning the Republican Party, Donald Trump today is expected to scurry back to the GOP and endorse frontrunner Mitt Romney (or perhaps Newt Gingrich).

The fungible nature of the purported billionaire’s political beliefs, of course, is one of the 65-year-old developer’s many bothersome traits. To call The Donald a weathervane is an insult to the stability of weathervanes everywhere.

But let’s cut to the documents.

Trump’s political flip-flopping over the past quarter-century is best chronicled in the files of New York City’s Board of Elections, where the businessman’s assorted voter registration cards are stored. Here’s what they reveal:

* In July 1987, Trump first registered from his penthouse in Manhattan’s Trump Tower. He enrolled in the REPUBLICAN PARTY, listing his prior residence as his boyhood home in Jamaica Estates, Queens.

* Twelve years later, in October 1999, Trump dumped the GOP, and enrolled in the INDEPENDENCE PARTY.

* Less than two years later, in August 2001, Trump again changed his party enrollment. This time, he emerged as a member of the DEMOCRATIC PARTY.

* He lasted eight years as a Democrat. In September 2009, Trump changed his affiliation, this time returning to the REPUBLICAN PARTY.

* As of press time, Trump’s latest party switch occurred six weeks ago, on December 21, when he again ditched the GOP. But instead of siding with a particular party, Trump checked off the box indicating “I DO NOT WISH TO ENROLL IN A PARTY.”