in DWILMINGTON, Del. — Addressing a nation consumed by crises, Jill Biden used her prime-time speech during the second night of the Democratic convention to make the case that her husband understood the urgent challenges facing American families — and that he had the experience and character to meet the moment.

Speaking from a classroom at Brandywine High School, where she once taught English in the 1990s, Dr. Biden described how the pandemic has disrupted education in the country, tearing at the fabric of families, communities and the economy nationwide.

“This quiet is heavy. You can hear the anxiety that echoes down empty hallways,” Dr. Biden said. “There’s no scent of new notebooks or freshly waxed floors. The rooms are dark as the bright young faces that should fill them are now confined to boxes on a computer screen.”

“I hear it from so many of you — the frustration of parents juggling work while they support their children’s learning,” she said. “The despair in the lines that stretch out before food banks, and the indescribable sorrow that follows every lonely last breath that follows when the ventilators turn off.”

Though Dr. Biden spent eight years as second lady of the United States, the speech offered a broader introduction to the wider American electorate that may not have been as familiar with the former vice president’s wife.

And for a while, that was by design. While Dr. Biden had a number of policy priorities as second lady, including championing military families and promoting community colleges, she was also focused on maintaining her own career. She worked as an English professor at Northern Virginia Community College throughout the eight years of the Obama administration and into the campaign, grading papers on airplanes and at events.

But Dr. Biden, who was a reluctant political spouse early in her marriage to Joseph R. Biden Jr. and had been skeptical of several previous discussions of presidential runs, was entirely on board with her husband’s 2020 campaign, allies say. And this cycle Dr. Biden has emerged as one of her husband’s most prominent and powerful surrogates.

“Before the pandemic hit, she maintained a public schedule that was sometimes more rigorous than Mr. Biden’s, hosting her own events and fund-raisers, and often speaking to Mr. Biden’s character. She has maintained those efforts through virtual events in recent months.

On Tuesday, as she capped a night that featured former presidents and two former secretaries of state, John F. Kerry and Colin Powell, Dr. Biden’s speech touched on more personal matters of grief and resilience. In 1972, Mr. Biden’s first wife and a baby daughter died in a car crash; in 2015 the Bidens lost their elder son, Beau, to brain cancer.

While Mr. Biden can be prone to making missteps in speeches, perhaps his greatest strength is his ability to empathize with others, a skill that allies say is rooted in part in his own experiences with family tragedy.

“There are times when I couldn’t imagine how he did it — how he put one foot in front of the other and kept going,” Dr. Biden said. “But I’ve always understood why he did it.”

“He does it for you,” she added.

Before she spoke, Dr. Biden appeared with Mr. Biden in an introductory video that told their story of how they met, and how they raised their family.

“I asked her to marry me five times,” Mr. Biden said. Dr. Biden replied that “I had to be sure that it had to be forever.”

For most of the video, the roles reversed: it was Mr. Biden heaping praise on Dr. Biden. “She is so damn tough and loyal,” he said.

Should Mr. Biden emerge victorious in November, one rhythm from the Obama administration will return to the White House: Dr. Biden plans to keep teaching.

“If we get to the White House, I’m going to continue to teach,” Dr. Biden said in an interview with CBS Sunday Morning.

It likely won’t surprise Mr. Biden. “Teaching is not what Jill does,” Mr. Biden said. “It is who she is.”