Shares plunged by more than 12 percent on Tuesday as investors and analysts speculated whether the company could halt its current sales collapse or even avoid a takeover.

Mr. Johnson wanted to transform Penney into shopping wonderland with designer boutiques and stable prices instead of coupons. But many of his ideas were not tested and soon backfired, and in recent months the board, including William A. Ackman, the activist hedge fund titan who had recruited him, grew impatient.

No sooner had Mr. Johnson been named as chief executive in 2011 than he began poking fun at Penney’s way of doing business. At a regular Monday sales meeting, “he was pretty sarcastic about our marketing and how ridiculous it was,” and he asked the chief marketing officer to count up in front of the group how many mailings were sent each week, said one former employee who, like others who spoke for this article, asked to remain anonymous to protect working relationships.

Mr. Johnson dismissed most of the top executives from Mr. Ullman’s reign and brought in his own team, largely from Apple and Abercrombie & Fitch. Mr. Johnson commuted from California, and employees said he was a hard worker, decisive and responsive to even late-night e-mails. But few of the top executives he had hired relocated to Texas, instead working there a few days a week, staying “quarantined,” as a veteran put it. Penney hands used the acronym AAPLE to refer to the newcomers — Apple & Abercrombie Paid to Lose Earnings.

Mr. Johnson liked to tell employees that there were two kinds of people: believers and skeptics, and at Apple, there were only believers. He wanted the same at Penney: when employees pushed back on Mr. Johnson’s strategies, they got nowhere, according to several former executives. Even when Mr. Ackman urged him to meet with retail stars like J. Crew’s Millard S. Drexler and Topshop’s Philip Green, Mr. Johnson seemed to pay little attention to their doubts.