What once was America’s Pastime by acclamation prepares for its showcase midsummer break on the nation’s biggest stage, in prime time, in New York.

This should be a time for our oldest sport to preen and be proud as it flexes its tradition and shows off its stars.

Instead, there is fetid air swirling in the buildup and the stink will hover dense over the Mets’ ballpark during the festivities, because, once again, our most historic game looks dirty. It looks embarrassed, and it should be.

The Home Run Derby?

The All-Star Game?

Who cares who wins? Why even play when we already know the result?

Baseball loses.

Baseball loses because cheating overshadows the excellence that is supposed to own the stage right now.

Baseball loses because two of the sport’s biggest stars, the Yankees’ Alex Rodriguez and the Brewers’ Ryan Braun, are about to be the headline names in a tidal wave of suspensions related to performance-enhancing drugs, each facing up to a 100-game banishment, according to ominous reports.

Baseball loses because four of the other players implicated in the scandal that arose from Coral Gables’ now-shuttered Biogenesis clinic are current All-Stars who will try to smile through their shame Tuesday night.

Baseball loses because — 15 years after Mark McGwire and Sammy Sosa’s home run-festooned and ill-fated Summer of Love — this sport’s Steroids Era is not yet past tense. Tense, yes. But not past.

One year ago while with the Giants, Melky Cabrera won an All-Star Game MVP trophy and then was suspended in August for 50 games for using PEDs. (He actually had tested positive before the ASG but had appealed, so, in effect, he played the game while out on bail.)

This time, baseball has four chances to duplicate that embarrassment, because All-Stars include the Padres’ Everth Cabrera, A’s Bartolo Colon, Rangers’ Nelson Cruz and Tigers’ Jhonny Peralta — all implicated in the Biogenesis scandal, and all facing imminent suspensions right along with A-Rod, Braun and some 20 players in all.

So much of baseball’s latest scandal is so Miami.

The notorious PED-peddling “clinic” run by Tony Bosch operated right across from UM. Braun had been a college star for the Hurricanes a short walk away … at the ballpark that now notoriously bears the name of Miami-raised A-Rod, a major donor.

Rodriguez, who first admitted past steroid use in 2009, was a certain first-ballot future Hall of Famer before his résumé and name were tainted by cheating.

Braun’s accomplishments in his 6 1/2 seasons also should point to Cooperstown: A Rookie of the Year honor, the 2011 NL MVP award, a home run title, five All-Star selections. But he, too, risks seeing that gilded future run away from him along with his good name, never to return.

There is a reason Hall of Fame voters and the public hold baseball’s PED crowd in such contempt.

Cheating in this manner requires much consideration, planning and cover-up, as well as the duplicity of others. It is the ultimate premeditated crime. The ballplayer convicted of an impaired-driving charge can at least claim it was a solitary lapse in judgment that had nothing to do with baseball. The ballplayer convicted of a PED can claim neither.

Braun’s implication in cheating hits particularly hard, I think, because he fits neither of the demographics you think of first when you think Steroids Era.