Facing off against Senator Bernie Sanders on Thursday night, Hillary Clinton did not comport herself like someone who had just suffered a landslide loss in New Hampshire. She did not raise her voice or express anger. She did not demonize Mr. Sanders or suggest he would be a dangerous choice for Democrats. She remained calm as he pungently sought to highlight their differences.

Instead, she behaved like someone heading into Nevada and South Carolina with every reason to be confident and little to fear but her own missteps.

A week after loudly confronting Mr. Sanders in a debate for perpetrating what she called a “very artful smear” against her, Mrs. Clinton took a far more strategic approach. She sought to portray her political approach as different from that of Mr. Sanders, a self-described democratic socialist, but her tone was firm but not panicked. For much of the night, a viewer could have been forgiven for thinking that it was Mr. Sanders who was grappling with the way forward after being handed a 22-point loss two nights earlier — and Mrs. Clinton who was riding high.

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The harshest critiques she had for Mr. Sanders were delivered coolly. She portrayed him as neither forthright nor realistic about how much his ideals would cost, and as an interloper in the Democratic Party who did not deserve to carry on the unfinished agenda of President Obama.

And she suggested that as often as he may point to his superior judgment in opposing the authorization of the use of force in Iraq in 2002, he was unprepared to deal with the wider global challenges the next president will face. “I do not believe that a vote in 2002 is a plan to defeat ISIS in 2016,” she said succinctly.

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Instead of dismissing Mr. Sanders’s plan for free college tuition as wrongheaded, she argued that it was unworkable.

“Senator Sanders’s plan really rests on making sure that governors like Scott Walker contribute $23 billion on the first day to make college free,” she said, invoking Wisconsin’s conservative governor, who slashed $250 million from the University of Wisconsin system last year. “I am a little skeptical about your governor actually caring enough about higher education to make any kind of commitment like that.”

It was a striking recalibration, and made for a far different presence compared with the combative posture Mrs. Clinton struck at last week’s debate and in the closing days in New Hampshire. And it may ultimately prove more effective.