If there's one thing A.J. Preller is known for, it's making blockbuster trades. From Juan Soto to Blake Snell to Mason Miller, Preller acquired as many stars as any executive in the sport. Some of these deals have worked out wonderfully, while others have left some to be desired. The deal that brought Josh Hader to the San Diego Padres fits into the latter bucket.

This isn't because of how Hader pitched. Sure, he struggled after the Padres acquired him at the 2022 trade deadline, but he pitched like the best closer in the sport the following year, allowing him to then sign a massive five-year deal with the Houston Astros. Instead, this has everything to do with what the Padres gave up to acquire Hader from the Milwaukee Brewers, mainly lefty Robert Gasser.

Robert Gasser is establishing himself right in front of our eyes in the postseason

The player most known for going to the Brewers in this deal is Esteury Ruiz, and that's mostly because he was later flipped in the deal that brought William Contreras to Milwaukee. This return for the best closer in the world didn't look great for Milwaukee for a while, but Gasser, who had a 3.87 ERA in 21 regular-season appearances, has been dominant in the playoffs.

He started Game 3 of the NLDS against the Padres and allowed one run in four innings. He started Game 3 of the NLCS against the Dodgers and allowed no runs on three hits in five innings. He then started Game 3 of the World Series against the Rays and allowed no runs on one hit in six innings, becoming the first Brewers starter to throw a pitch in the sixth inning this postseason and faced the minimum during his six completed frames.

It's easy to overlook him in a rotation that includes Jacob Misiorowski and Logan Henderson, but he's out-pitched both in the postseason, pitching to a 0.60 ERA in his three starts. All three of those starts have come in important games on the road. All of a sudden, the 27-year-old southpaw is looking like a viable mid-rotation starter for a Brewers team that continues to churn out starting pitchers like it's nothing.

Padres regret trading Robert Gasser to Brewers in hindsight

It's easy to play the hindsight game. I think most Padres fans were thrilled when they made this trade, and again, Hader was really good for the team in 2023. In hindsight, though, boy, could the Padres have used a pitcher like Gasser.

Does he have ace upside? Almost certainly not. I wouldn't even really want him as a No. 2 starter. But mid-rotation arms are incredibly valuable, and I do think Gasser is that, or at least is on his way to becoming that. Given the state of the Padres' rotation (Joe Musgrove projects to be their ace in 2027, with Jagger Hayes as their No. 5 starter), Gasser could've really come in handy, especially on a minimum salary.

Part of what trading prospects for established stars does is risk said prospects blossoming in another organization. Had the Padres known what Gasser would become, they likely would've held onto him, even if it meant not getting Hader. That felt obvious after Gasser pitched well against them this postseason, and feels even clearer now, when looking at how well he pitched in the Fall Classic, and how dire the Padres' 2027 rotation situation is.