BOSTON — Faced with questions about her viability in a general election and ceding ground to opponents in the primary, Senator Elizabeth Warren is abandoning her above-the-fray approach and delivering her most forceful and direct criticism yet of her Democratic opponents.

That is one of a series of adjustments Ms. Warren is implementing as she seeks to recapture the energy and excitement of the late summer and early fall, when she emerged as a top contender for the nomination. Over much of the last two months her ascent has stalled as opponents, led by Mayor Pete Buttigieg of South Bend, Ind., have questioned her stance on “Medicare for all” and portrayed her far-reaching policy agenda as a ripe target in a potential matchup against President Trump.

Now Ms. Warren and a Boston-based campaign team that has long resisted snap reactions to the day-to-day developments of the primary is nodding to the reality of a reshuffled race with no true front-runner. Her campaign is leaning into her role as the leading woman in the race and she is directly engaging with Mr. Buttigieg, after months of preferring to pick fights with the billionaire critics of her populist proposals.

Entering December, Ms. Warren has overhauled the format of her town halls in pursuit of more organic moments to connect with voters. She has zeroed in on the billionaire former mayor of New York City, Michael R. Bloomberg, as a leading villain in her tale of corruption and inequality in America, running an ad and appearing on his own television network to needle him.