If there is an upside to the decades of mediocre baseball that the Chicago Cubs have played, it’s that the expectations of their fans have been lowered to the point that any success is a welcome surprise. For years, the Cubs have focused on selling the Wrigley Field experience with its Old Style-soaked nostalgia and “Take Me Out to the Ball Game” and hey, if they made the playoffs every now and again, that was a pleasant bonus.

But times have changed. Since Chicago came within a Steve Bartman of making the World Series two years ago, the team’s nightmares of mediocrity have been replaced by dreams of Cy Youngs and no-hitters, inspired by its tremendously talented trio of young starting pitchers.

Between them, Mark Prior, Kerry Wood, and Carlos Zambrano won 55 games for Chicago in 2003, leading them into the playoffs, past the Atlanta Braves, and nearly into the World Series. It was easy to imagine the three becoming one of the great rotations of all time, especially with the addition of Greg Maddux as the fifth starter in 2004.

But things didn’t work out that way. Wood and Prior were struck with injuries and pitched only 140.3 and 118.7 innings in 2004, respectively. Zambrano, however, was exceptional, going 16-8 with 1 2.75 ERA. But Zambrano couldn’t carry the team, which dropped seven of its last nine games in 2004 to end up channel-surfing at home in October.

Which brings us to 2005. St. Louis was the popular choice to win the NL Central entering the year, and the Cards haven’t disappointed. They’ve jumped out to a 58-32 record and a 13-game lead over the Cubs. No, the surprise isn’t that St. Louis has been so good; it’s that Chicago has been so middling. To this point in the season, the Cubs have been a .500 team, and proved once again that they’ll go only as far as their starters can carry them.

Zambrano has pitched reasonably well, leading all Cubs pitchers with a 23.5 VORP (Value Over Replacement Player, or the number of runs Zambrano prevents above what a waiver-wire level player would add).Unfortunately, that’s just 30th-best in the major leagues, and when your best pitcher is putting up the 30th-best performance in the game, it shouldn’t come as a surprise if you’re hovering around the .500 mark.

The concern with Zambrano has been twofold: durability and control. Manager Dusty Baker has worked Zambrano like an indentured servant the past few years; the 24-year-old has averaged well over 100 pitches a start during his career. So far, Zambrano hasn’t faltered under his heavy workload, but given the starts missed by his rotation-mates, you have to wonder if Baker is playing with fire. Zambrano’s control has also been a concern. He strikes out over eight batters every nine innings, which is excellent. Unfortunately, he also walks more than four hitters per nine innings.

Meanwhile, both Prior and Wood have been limited by injuries. Prior missed the first two weeks of the season with an inflamed right elbow, then missed another month with a fracture of that same elbow from a liner hit by Colorado’s Brad Hawpe on May 27. When Prior has been on the mound, he’s been very good, going 6-3 with a 3.07 ERA in 13 starts, enough for a 21.6 VORP in that limited duty. His strikeout-to-walk ratio is a sparkling 3.48, which is good to see, given his struggles to locate his curveball at times last year. If Prior stays healthy and manages to dodge line drives, he should have a big second half and pitch like the Cy Young contender everyone thought he would be this season.

That brings us to the enigma that is Kerry Wood. At his best, he’s nearly unhittable. At his worst, he’s nearly unwatchable. Perhaps it’s time for Cubs fans to recognize that Wood isn’t a superstar who just needs to find that last secret to take himself to the top of the game. Instead, at 28 years old and in his seventh season, Wood is beginning to look like a good pitcher who can have great days rather than a great pitcher who can sometimes struggle. A 70-52 career record with a 3.67 ERA isn’t anything to be ashamed of, but given the expectations that have swirled around Wood since that day in 1998 when he struck out 20 Houston Astros, it seems like a disappointment.

Wood has missed almost two months this season with trouble in his throwing shoulder. He’s returned to the mound with revamped mechanics that he hopes will help him throw strikes more consistently, and stay off the DL, but a major mechanical revamp in mid-season doesn’t inspire much confidence.

Despite all the pitching upheaval (it’s not a good sign that John Koronka has started three games), the Cubs are only five games behind Atlanta for the wild-card lead. Now that they have their rotation back the way they imagined it, can they claw their way back into the postseason?

It’s not outside the realm of possibility. Teams have certainly come back from much farther to make the postseason; even last year, the Houston Astros were 14 games back in the wild-card race, and went on to make it to the NLCS. But the Cubs just seem to have too many question marks to be likely to repeat. They would need everything to go right for them the rest of the year – Derrek Lee is going to have to keep hitting like Babe Ruth, several teams ahead of them are going to have to falter, and most importantly, their starters would all need to be lights out. It’s not hard to imagine a couple of those things happening, but usually, when a team needs all of the stars to align to keep their hopes alive, there’s a stubborn one that won’t lock into place.

Prior, Wood, and Zambrano will be back in the postseason. It just won’t be in 2005.

Mr. McClusky is a writer for Baseball Prospectus. For more state-of-the-art commentary and information, please visit baseballprospectus.com.