Elizabeth Warren had never taken on the federal government before.

But in 1995, she found herself up against the Clinton administration, representing the Cleveland-based conglomerate LTV Steel.

Even though LTV had sold off its coal mines during the 1980s, a new law required it to contribute to a health fund for retired miners.

LTV believed that it should not have to pay. Those claims, the company said, should have been handled as part of its bankruptcy reorganization.

Ms. Warren’s job was to convince the Supreme Court to hear LTV’s case.

The court declined, but for Ms. Warren, the issue would fester. Over a decade later, when she ran for the Senate from Massachusetts in 2012, the Republican incumbent, Senator Scott Brown of Massachusetts, tried to use her work for LTV against her, unleashing an ad calling her a “hired gun” who sided “against working people.” Notwithstanding the attack, Mr. Brown lost his seat to Ms. Warren.