The Cajun Electric Power Cooperative filed for bankruptcy in the 1990s, creating a juicy target for companies eager to snatch up its operations, including the coal-burning “Big Cajun” plant with its massive carbon footprint near Baton Rouge, Louisiana.

One eager suitor was Southwestern Electric Power Co., which went to court trying to halt its sale to a competitor. Among the white-shoe lawyers representing Southwestern Power was then-Harvard Law School professor Elizabeth Warren.

To hear Ms. Warren explain it years later, she was a white knight swooping in to save Cajun and protect local Louisiana jobs.

That is almost exactly the opposite of what she was doing, said another lawyer involved in the proceedings. He said it was just another high-powered corporate vulture picking over Cajun’s carcass.

“Her client was a large power company that wanted to liquidate the cooperative, not to save it,” New Orleans lawyer Matthew Farley said.

“I don’t know what was going through her head, but she did in fact appear and argue on behalf of a large utility whose objective was to buy the [then] coal burning and natural gas burning assets of Cajun,” Mr. Farley said. “There’s nothing wrong with that — I was doing exactly the same thing for a competing utility — but this was big-ticket, hard-fought corporate litigation, nothing more or less.”

Ms. Warren revealed her work for Southwestern in 2012 as she mounted her campaign for the Senate seat she would go on to win, providing a partial list of clients to The Boston Globe.

Now, as Ms. Warren sets her sights on the White House, she has clammed up about her work. Over the past two weeks, her team rebuffed inquiries from The Washington Times for an updated client list and ignored requests to discuss her work for clients that are already public, such as Southwestern Electric.

Seven years removed from private life, Ms. Warren still downplays her $675-an-hour corporate legal work, which she did on the side of her academic career that began at the University of Pennsylvania in 1987 and continued at the University of Texas and Harvard Law School.

She has invariably cast her efforts as designed to help the underdog or save jobs when her ethical duty would have been to help her client.

Some of her legal work is likely to draw scrutiny from her fellow Democratic candidates, whose appetites are already whetted by the senator’s bungling of other parts of her history.

When it was revealed that Ms. Warren, operating out of her Harvard Law School office, did not have a license to practice law in Massachusetts, she insisted first that she wasn’t operating as a full-scale lawyer and then that she never practiced in a Massachusetts courtroom. Court records showed both claims were inaccurate.

In that sense, her accounts of her work as a corporate lawyer mimicked the versions she would tell of her American Indian heritage: The stories changed as more evidence undercutting them emerged.

In one prominent case, Ms. Warren described her defense work for the Travelers Insurance Cos., which records show earned her more than $200,000, as an effort to make sure plaintiffs were compensated.

Jim Barnett, a Republican campaign consultant who worked with Ms. Warren’s 2012 opponent, then-Sen. Scott Brown, called the explanations of her work “patently absurd.”

Such Fortune 500 work is certain to be re-examined as Ms. Warren campaigns for president.

“There has been very little focus since 2012 on Warren’s legal work while a law professor to protect large corporations,” said William A. Jacobson, a law professor at Cornell University who has been a longtime critic of Ms. Warren at his Legal Insurrection blog. “Now that she is running for president on a platform against large corporations, the hundreds of thousands of dollars she made representing those large corporations is a fair subject of scrutiny.”

One case that did prove damaging in her first foray into electoral politics was her representation of LTV Steel in 1995. She wrote a Supreme Court brief on behalf of the company, which was trying to avoid payments to a fund for retired coal workers.

Ms. Warren’s campaign said she was paid $10,000 for that work and cast her labors as an effort to preserve the rights of future victims.

But The Boston Globe and Boston Herald saw the case differently in 2012. They reported that Ms. Warren was defending a company trying to avoid paying into a health care benefits fund for retired coal miners.

Ms. Warren was a bankruptcy specialist, and many of the cases in which she participated involved companies coming out of bankruptcy, or their successors, arguing over whether they had to fulfill pre-bankruptcy obligations.

That often left her having to pick between aiding corporations, which were trying to avoid claims, or victims, who wanted the companies to make good on their promises.

Such a legal quandary presented itself in her representation of Dow Chemical Corp. in 1995, when the company faced bankruptcy because of a flood of lawsuits over silicone breast implants.

Ms. Warren left Dow Chemical off her 2012 list of clients. After Mr. Jacobson’s blog revealed her representation, she spun her work for the industrial giant as instrumental in setting up a $2.3 billion trust to pay women who said they were injured by the implants.

That explanation, though, doesn’t jibe with her duty as an attorney for Dow, where she was bound to represent the company’s interests.

“The notion that Warren was representing anyone other than her client is preposterous,” Mr. Jacobson said. “As an attorney, she had a duty of loyalty to Dow Chemical. If she explored possible ways in which Dow Chemical could extricate itself through settlement, her services were on behalf of and for the benefit of Dow Chemical, not the women.”

He said that for all the attention Ms. Warren received over her claims of American Indian heritage, her corporate work is a bigger vulnerability in the primary.

“The cumulative effect will be to destroy her credibility in a way that makes her appear unelectable against Trump when electability is an unusually important consideration for rank-and-file Democratic voters,” he said.

In a 1994 case involving Fairchild Aircraft Corp. when Ms. Warren was teaching at Penn, she consulted on the question of whether a company was liable for the crash of a plane owned by an earlier iteration of Fairchild.

The Warren campaign told The Boston Globe before a 2012 debate that her work was designed to help the little guy in the proceedings, but Mr. Jacobson’s analysis showed that her aim was to protect Fairchild from litigation filed by crash victims.

Colin Reed, a Republican Party consultant who has long tracked Ms. Warren’s career and considers her a formidable politician, said a Democratic opponent could do serious damage by using Ms. Warren’s legal career against her.

“She could wind up the victim of her own creation because she’s the one who gave birth to all this anti-capitalism dominating the Democratic discussion and it’s that same capitalism that she was engaged in and profiting handsomely from,” he said.

Nevertheless, Ms. Warren’s versions of events haven’t kept her from electoral success, as her two senatorial victories attest. Even Mr. Farley, who was complimentary of Ms. Warren’s skill in oral arguments before the 5th U.S. Circuit Court of Appeals, said he is not opposed to her political advancement.