When assessing the “former manager” wing of the Mets’ search for Mickey Callaway’s successor, you start with a simple, crucial question:

What went wrong?

How and why did each gentleman’s title downgrade from “Manager” to “Former manager?

Buck Showalter posted a ghastly 47-115 record with the 2018 Orioles. Joe Maddon generated diminishing postseason results (or lack thereof) from the Cubs for three straight seasons. Mike Scioscia qualified for the playoffs once in his final nine seasons with the Angels.

Joe Girardi? Oh, he took the Yankees to Game 7 of the American League Championship Series and saw a bunch of young players flourish on his watch.

That last one kind of stands out among the crowd, doesn’t it?

When evaluating Girardi — who, The Post’s Mike Puma reports, has been doing his homework on the Mets and has proclaimed his interest in managing again after two years off — the Mets must look in the mirror and acknowledge, “We ain’t the Yankees.”

The Yankees outgrew Girardi (and, let’s face it, the ultra-intense Girardi would wear out even the ultra-affable Brandon Nimmo after 10 years). The Mets, to their credit, outgrew Callaway, and Girardi would give them the greatest amount of the component they need most both in their clubhouse and among their fan base:

Credibility.

Or do you think four World Series rings (three as a Yankees player and one as their manager), don’t get folks’ attention?

When the Yankees opted not to extend the free agent Girardi after their 2017 run, general manager Brian Cashman cited “connectivity and communication” as the reasons, and he proceeded to hire Aaron Boone, who has excelled in those departments, as Girardi’s replacement. No one would dispute that Girardi’s greatest attribute is not his connectivity and communication, but rather his ability to manage the actual games.

Again, though, look at that ’17 season that got Girardi canned: Aaron Judge won American League Rookie of the Year honors and finished second in the AL Most Valuable Player vote. Gary Sanchez’s first full big-league season ebbed and flowed, lowlighted by Girardi pulling the catcher from a game due to defensive incompetence, yet concluded on a high note. Luis Severino placed third in the AL Cy Young vote.

The team played with a looseness and established a bunch of silly, playful routines like the “thumbs down,” pointing back to the dugout after a big hit and the “Toe-night Show,” with Didi Gregorius and “cameraman” Ronald Torreyes “interviewing” teammates following offensive heroics.

Whatever Girardi’s failings were, they didn’t quite paralyze the club. Throughout his decade running the Yankees, he showed himself intelligent enough to work on notes from Cashman, be they lightening up with his players or exhibiting more patience with the media.

Now, about his intelligence and patience, the elephant in this room is how Girardi could coexist with Mets general manager Brodie Van Wagenen and owners Fred and Jeff Wilpon. After all, Girardi lasted only one year with micromanaging Marlins owner Jeffrey Loria before getting fired (he nonetheless won National League Manager of the Year honors that year, 2006). Those relationships will largely determine the fate of whomever the Mets hire.

Out of the gate, at least, goodwill exists. Girardi, deploying the same fox-in-the-henhouse strategy as Boone by working as a broadcaster, conversed briefly and amicably with Van Wagenen and Jeff Wilpon prior to at least one 2019 Mets game at Citi Field for which he was providing commentary. With these Mets, who saw many interesting candidates pass on interviewing as their GM a year ago because of the organization’s negative reputation, that ranks as a victory.

Getting Girardi to manage them would be the equivalent of convincing Sandy Alderson to be their general manager nine years ago, a move that still pays dividends with the trove of young talent Alderson acquired, which increases the appeal of this managerial opening.

After all, the Mets would sell their souls for a “What went wrong?” story like Girardi’s pinstriped departure.