What would you do: Supervisor promoted the wrong person

Periodically, we present a real-life workplace problem and ask three HR managers to provide a solution. This week’s problem: A supervisor has “buyer’s remorse” over the selection of an employee for promotion.
The scenario
“Sandy, you gotta help me,” said supervisor Tom Bartley. “I really screwed up.”
“What’s the deal?” asked HR manager Sandy Gomez, motioning for Tom to take a seat. “Problems in the department?”
“Yeah, you could say that. It all boils down to this: I promoted the wrong person, and I can’t think of a good way to fix the situation.”
Things didn’t go as planned
“I remember when you were agonizing over who to choose – Rebecca or Trish,” Sandy recalled. “I guess Rebecca hasn’t worked out as well as you’d hoped.”
“Boy, that’s an understatement,” said Tom. “She just can’t seem to get the hang of her new responsibilities. And the more she screws up, the more defensive she gets. And then everybody in the department starts getting an attitude. It’s a mess.”
“What’s Trish’s reaction been?” Sandy asked.
“She hasn’t said a word,” Tom answered, “but I’ve caught some of her facial expressions when things have gone wrong.
“She knows we can’t continue to operate like this. And the other employees know it, too.
“I’m going to have a revolt on my hands if I don’t do something soon,” Tom concluded. “The question is, just how am I going to finesse this? I’d hate to lose Rebecca, but she’s making everybody’s life miserable.”
If you were Sandy, what would you advise Tom to do next?
Ron Wolfgang, HR manager, South Bend, IN
What Ron would do: I’d have Tom set up a 30-day performance plan for Rebecca. It’ll need to be clear and concise, so Rebecca understands what she needs to improve on. She also needs to understand that if she doesn’t make improvements by the end of 30 days, there will be some changes.
Reason: I hate to not give employees an opportunity to improve their productivity. So giving Rebecca a month to turn around her efforts is the best remedy. But after that, we can’t afford to have her continue performing poorly.
John Steepy, HR manager, Rochester, NY
What John would do: I’d make sure that Tom has documented all of Rebecca’s shortcomings. If so, either demotion (if she agrees) or termination would be my recommendation.
Reason: As long as there’s documentation, a demotion or termination is the natural response to an employee not pulling his or her weight. Morale and productivity can’t be sacrificed.
Jean Yarger, HR manager, Grafton, WI
What Jean would do: First, I’d have Tom ask Rebecca how she thinks she’s performing. If she admits to her poor job performance, I’d suggest either handing Rebecca her old job back or lightening her duties in favor of more work for Trish. If Rebecca doesn’t realize she’s performing poorly, I’d advise Tom to set specific performance goals for her.
Reason: It’s always wise to see how an employee rates his or her own production before taking drastic measures. It’s a safeguard against a possible lawsuit. After that, you look for a solution that’s in the best interests of the company.