Michael Bloomberg speaks at the Global Action Climate Summit in...

Michael Bloomberg speaks at the Global Action Climate Summit in San Francisco last month. Credit: AP / Eric Risberg

Conventional wisdom says former New York City Mayor Michael Bloomberg doesn’t have a shot at the Democratic nomination for president in 2020, and being “a short, Jewish, divorced billionaire” has nothing to do with it.

In case no one’s noticed, lots of Democratic primary voters, much like their GOP compatriots, have flipped their collective lids of late, leaning toward the angriest, most fiscally irresponsible candidates to represent them in Washington.

Mike Bloomberg is neither.

Besides, wasn’t Bloomberg a Republican mayor? How does one wash his clothes of ‘dem cooties in 21st century Democratic politics?

One doesn’t, is the answer.

Convention has never bound Bloomberg. Defying it has been his trademark: Fired from red-hot Salomon Brothers in 1981, a then 39-year-old Bloomberg turned his severance check into a venture that would revolutionize Wall Street and make him one of the wealthiest people in the world. Then, out of nowhere in 2000, the previously apolitical Democrat billionaire began making his way around New York City Republican circles, talking about the mayoralty. No one took him seriously. His run was a vanity project, we said.

A year into Bloomberg’s first term — he would be elected to three — Salomon folded.

But winning a partisan, rough-and-tumble national primary is a far taller order, and the 2020 Democratic primary is shaping up to be more rodeo than horse race. More than 20 Democrats have expressed interest in running, a field potentially larger than the 2016 Republican primaries.

Bloomberg’s 69-word Instagram post Wednesday announcing his return to the Democratic fold hints at how he might plan to ride into it: As himself. Unabashedly.

“At key points in U.S. history, one of the two parties has served as a bulwark against those who threaten our Constitution,” Bloomberg wrote. “ . . . Today, I have re-registered as a Democrat — I had been a member for most of my life — because we need Democrats to provide the checks and balance our nation so badly needs.”

The key phrase is the reference to checks and balances. That has long been a theme for Bloomberg. Assuring checks and balances in 6-1 Democrat-to-Republican New York City was a reason cited for his running as a Republican outsider 18 years ago. There is a consistency there that works.

With enough left-wing candidates in the 2020 field, a lane should be available for a “short, Jewish, divorced billionaire” — Bloomberg’s words to poke fun at himself — with liberal values, fiscal pragmatism and a penchant for getting things done. He’s also got 51 billion bucks to sell his message, which helps. And that’s not even counting his change jars.

The 2020 primary calendar helps, too. Delegate-rich California, with 11 media markets, will hold its primary on March 3 instead of June 7 — just three weeks after New Hampshire — giving candidates with the means to advertise there a major opportunity to snatch early momentum. Bloomberg’s native state, Massachusetts, casts its votes the same day. Moreover, the number of states holding Democratic caucuses instead of primaries — caucuses disproportionately turn out hard-core liberals — will be reduced from 14 to 7 in 2020. All those things work to Bloomberg’s advantage, as does a large primary field.

The Democratic presidential primaries are both right around the corner and 100 years away. Anything can happen between now and the Iowa caucuses (Feb. 3). But one thing is for sure: If Bloomberg goes all in on the race, all bets are off for a hard-left Democratic nominee. That could change everything in a general election matchup.

William F. B. O’Reilly is a consultant to Republicans.