The Cardinals’ bullpen reminds me of a line from The West Wing: “The most costly disruptions always happen when something we take completely for granted stops working for a minute.”

You’d forgive St. Louis and manager Mike Matheny for taking Trevor Rosenthal for granted. From the moment he stepped on a big league mound in 2012 until last month, the 26-year-old closer had been as trustworthy a relief pitcher as you’ll find. But since June 3, when Rosenthal allowed three earned runs without retiring a batter, he’s posted an 8.27 ERA and allowed a .483 opponent OBP, walking 14 batters, and raising his ERA by more than three runs in only 16.1 innings. He’s lost the closer role to Seung-hwan Oh, and earlier this week, he landed on the DL with inflammation in his throwing shoulder.

On some level, Rosenthal being hurt must be a relief, because not only does it provide a possible cause for his loss of effectiveness, but it also allows Matheny to shift to a bullpen paradigm that doesn’t involve trying to fix Rosenthal and win games at the same time.

A team that loses trust in its closer can suffer in three cascading ways: (1) The guy you rely on to pitch your highest-leverage innings is blowing leads. (2) The replacement closer himself isn’t any good (otherwise, he would’ve been closing in the first place). And (3) everyone left in the bullpen is suddenly pitching more important innings than he had been before.

The Cardinals’ bullpen has the lowest net win probability over the course of the season among playoff contenders, and that’s largely because Rosenthal’s WPA of minus-1.75 is the worst of any relief pitcher in baseball this year. St. Louis hasn’t had any problem with Rosenthal’s replacement: Oh is striking out 11.6 batters per nine innings with a 243 ERA+, and he brings with him 11 years of professional experience as a closer in Korea and Japan, where he earned the nickname “the Final Boss.” But the knock-on effect of moving up the rest of the relief staff — Jonathan Broxton, Seth Maness, Tyler Lyons — has weakened the bullpen in the middle innings.

The Cardinals are still 55–47 and right in the thick of the wild-card race because GM John Mozeliak can produce average to above-average position players with such frequency that you’d have to assume he was granted the power of divination as a child. But Mozeliak hasn’t been able to conjure a complete bullpen this season.

The Cardinals have other problems: Kolten Wong has been inconsistent, Matt Carpenter and Jhonny Peralta have been hurt (but should return soon), and Matt Holliday and Yadier Molina are slowing down. But the bullpen is the easiest problem to fix. Mozeliak doesn’t need Andrew Miller or Wade Davis — just one or two more guys Matheny can trust in the middle innings.

Mozeliak could go out and spend on someone like Milwaukee’s Jeremy Jeffress or Philadelphia’s Héctor Neris, or take a flier on pitchers like the Angels’ Huston Street or Joe Smith. Or he could look at the option right in front of him.

The 21-year-old Alex Reyes is a right-handed pitcher for Triple-A Memphis, and he might be the missing guy. Born and raised in New Jersey, Reyes moved to the Dominican Republic as a teenager, and became an international free agent, sidestepping the draft. In December 2012, the Cardinals gave Reyes a $950,000 signing bonus, and since then, he’s been one of baseball’s top pitching prospects. Despite struggles with his control — he’s posted a BB/9 of 4.3 or higher at every minor league level — and a 50-game suspension after his second positive test for marijuana use (a drug which big leaguers aren’t randomly tested for) this past offseason, MLB Pipeline just rated Reyes the no. 9 prospect in all of baseball. Baseball Prospectus’s midseason update had Reyes at no. 8, and ESPN’s Keith Law had him at no. 19. He is the top pitching prospect who has yet to make his big league debut.

What makes Reyes so special? Take a look at his start in the Futures Game a few weeks ago.

Reyes still has to improve his command and his changeup to maximize his potential as a starting pitcher, but the Cardinals don’t need starters right now. They need a guy who can come in and pitch a clean seventh inning. In short stints, like his turn in the Futures Game, Reyes can pop his fastball up to 101 mph, then work off that to a hard-breaking, low-80s curveball. (Forget the break on the curve, the speed differential alone makes that tough to hit.) Reyes is still months, maybe a year away from being ready to start in the big leagues, but he can come up now and make an impact out of the bullpen, where command and pitch variety matter less since you’re rarely facing any batter more than once.

Plus, he can do it at minimal risk to his long-term development. There’s a long list of pitchers like Reyes (Brandon Finnegan, David Price, Aaron Sanchez) who came up in situations like these and pitched well before taking their place in a starting rotation. In fact, the Cardinals don’t even have to look outside their own organization for similar success stories: Carlos Martínez and Adam Wainwright both started out in the bullpen because of organizational need.

Mozeliak should explore all options for improving his team, and if he can get good deals, he should try to pick up all the quality pitchers he can. But Reyes costs nothing to acquire, and he has as much upside as any reliever on the market short of Miller or Davis. If he doesn’t work out, Mozeliak can send him back down and try something else, but if he does work out, Matheny will be able to fill that Rosenthal-shaped hole in his bullpen.