Target Corp.'s grocery chief, one of CEO Brian Cornell's first major hires, is leaving after just 18 months in the role.

The departure of Anne Dament, Target's senior vice president of grocery merchandising, comes as the Minneapolis-based retailer continues to struggle through an overhaul of its grocery department.

Meanwhile, a growing roster of rivals continues to step up its food game.

The makeover of Target's grocery aisles, an effort that started nearly two years ago, has taken longer than expected to materialize.

And the changes that have been rolled out to stores, including adding hundreds of gluten-free and organic items to its shelves, have apparently not yet impressed shoppers enough.

In August, Target reported a surprising 2.2 percent drop in traffic and a 1.1 percent slide in comparable quarterly sales. Executives blamed the lower performance in part on its grocery business as well on the transition of its pharmacies to CVS and a slowdown in electronics sales. They also acknowledged they hadn't done well enough in emphasizing low prices in store displays and circulars and promised to fix that going forward.

Still, they said they expect those challenges to haunt them for the rest of the year and lowered their forecast for the coming months to flat, due to lower sales.

Target did not elaborate on the circumstances around Dament's exit. Her last day will be Nov. 18, said company spokeswoman Katie Boylan.

Her work is already being transitioned to Mark Tritton, Target's chief merchandising officer and Dament's boss. At the same time, Boylan said, Target is launching a comprehensive search for a replacement that will include internal and external candidates.

"There's a little bit of surprise because this was Cornell's person," Brian Yarbrough, an analyst with Edward Jones, said of Dament's departure. "But on the other hand, the results on the grocery side have not been good."

As Target looks for a new grocery leader, he wondered if that means Target might also alter its strategy.

"They're just in a really tough spot," Yarbrough added. "They don't have enough groceries to drive people to the store regularly. Groceries for Target never turned out to be a destination like they thought it would be."

Groceries have always been a bit of a conundrum for Target. Several years ago, Target remodeled most of its stores to include an expanded grocery assortment even after deciding not to turn all of them into full-blown SuperTargets. But executives acknowledged that the retailer found itself in a sort of "no man's land" in being neither a specialty grocer like Trader Joe's nor a full-service grocery store like a Wal-Mart or Cub Foods.

Still, food is a big part of its business, accounting for about 20 percent of its sales.

Cornell joined Target in August 2014 with an extensive grocery background, including positions at PepsiCo, Sam's Club and Safeway, raising analysts' expectations that he would help Target figure out its niche in food.

In April 2015, he hired Dament, a colleague from Safeway, to oversee the food business.

"Having previously worked alongside Anne, I know her industry expertise and proven ability to reinvigorate existing businesses make her the right leader to drive our reinvention," Cornell said in a statement at the time of her initial appointment.

In January, Target also moved Aaron Alt, who helped wind down Target's Canadian business, to a new role as senior vice president of grocery transformation, a position that included more long-term and operational planning. He worked closely with Dament and will continue in that role for now. But the company hopes the new grocery leader will be able to fill both positions.

In addition to adding more organic and natural items, Target also has been doubling down in key categories for fill-in trips such as snacks, yogurt and craft beer. Plus, it has worked to improve its fresh products through closely examining its supply chain and sourcing.

While the new products Target has been adding to its aisles have not yet translated into better sales, Cornell had remained upbeat about the overall direction, noting that it may take awhile for shoppers who were turned off from Target's grocery aisles in the past to give them another try.

"It's just going to take time for us to get credit for those changes," he told reporters in September. "It's not going to happen overnight."

At the same time, he emphasized that Target is not looking to become a full-service grocer with butchers and sushi chefs, but it will continue to be a place where people can grab a new outfit and a gallon of milk at the same time.

Target has been testing some cosmetic changes to its grocery departments in Los Angeles and Dallas area stores that include fancier lighting and display bins more reminiscent of a farmers market. In select markets, Target also has added grocery directors with their own dedicated teams.

At the same time, competitors such as Wal-Mart also have been improving their fresh produce and lowering prices, moves that appear to be paying off with higher sales.

Dament, who grew up in the Twin Cities and started her career as a buyer for Eden Prairie-based Supervalu, is the third senior executive to depart Target in recent months. In August, Jeff Jones, Target's chief marketing officer, took a job as president of Uber. Target's chief digital officer, Jason Goldberger, left the company in September.

The retailer, whose third quarter just ended, will report its results on Nov. 16.