ST. HELENA ISLAND, S.C. — Amid continuing attacks on her family, Jill Biden has a simple message for President Donald Trump: “Stop it. My husband's going to beat you.”

In an exclusive interview with NBC News on Monday, Jill Biden said that the efforts by the president and his Republican allies to draw her extended family into the campaign will backfire. But she also acknowledged that the attacks have gone beyond even what she expected.

“The fact that he attacked my son, I have never seen that in other elections, that they go after children of the candidate,” she said. “He's just trying to distract the voters. You know what Donald Trump did was wrong, flat-out wrong. Calling a foreign leader and asking them — and holding back foreign aid unless he investigated my husband, my son — that is just flat-out wrong and I think that the American people see that, I think the people in Congress see that and they're going to stand up to him.”

Her comments came as part of her first extended solo national interview of the campaign, as she stumped for her husband in this must-win state for the former vice president. And they come as the president and Republicans in Congress have called for Hunter Biden to testify in the House impeachment hearings beginning this week about his past business dealings in Ukraine.

By her own admission, Jill Biden was “never a natural as a 'political spouse,'” writing in her memoir released earlier this year that she “preferred to stay in the background” early in Joe Biden's political career and even more so when the national spotlight turned on them in 2008.

But there has been a marked change in her campaign trail performance as she shares more personal stories about her and her husband, surprising even him at an event in New Hampshire on Friday by talking about his family upbringing. She’s also shown a feistier side.

At a rally with her husband before the recent Iowa Liberty and Justice Celebration, she immediately launched into a story about the time she punched a neighbor who had been bullying her sister.

“I hate bullies,” she said. “Nothing make me angrier than seeing someone abuse their power to make others feel small.”

On Monday, Jill Biden wouldn’t go so far as to say Trump was a bully, but made it clear how she views him.

“Donald Trump and Joe Biden are just polar opposites," she said. "And that's why I think people are looking for the qualities in a leader — they want a strong leader, they want a resilient leader,” she said.

In his long career, Joe Biden has cultivated a reputation for his authenticity. But former and current Jill Biden staffers universally describe her as “a real person” in a different context, noting both her reticence toward traditional politics, her occasionally rebellious and subversive sense of humor and her passion for Philadelphia sports and her own career.

As with her husband, sometimes that realness can backfire. She raised eyebrows this summer when she told an audience of Democratic and independent voters in New Hampshire that they might have to “swallow a bit” and support her husband even if they might like another candidate better.

Jill Biden said Monday that comment was misconstrued, as she spoke specifically to an audience who had already shared with her whom they were supporting. But she did say electability was still critical.

“I think the beauty of our political system is that anybody can get in to run for president, but I think Joe is the best qualified. I think he's ready on day one. He's steady, he'll be a steady commander in chief. And he knows the job, he has experience, he's ready on day one,” she said.

Biden downplayed her role as an adviser to her husband but made it clear she would continue to advocate on the issues important to her, especially education and veterans.

She decided this summer to continue her teaching career even as she expected to step up her time on the campaign trail. She will face another decision again soon about whether to continue in the spring semester, just as voters will be determining the nominee in primaries and caucuses across the country.

In 2009, she became the first "second lady" to continue her professional work into the White House. What Jill Biden is not yet clear about is whether she can do the same if her husband returns there as president.

“How great would that be? What would that say about teachers? Wouldn't that lift up the profession and celebrate who they are? It would be my honor,” she said.

Jill Biden says her time on the campaign trail has already affected her in ways she didn’t expect. In her book, she describes struggling with her faith after Beau Biden’s death, how it drew her husband closer to the church but pushed her away. But during a trip with her husband to a South Carolina church, she found surprising comfort in the experience.

“I think so many people have prayed for me that I need to return that, that kindness to others as well. So I'm working my way back,” she said.

But she added that she still thinks about Beau every day, including how this campaign might have been different if he had beaten cancer.

“You know Beau was so involved in the process, he so wanted his dad to be president,” she said. “I thought maybe this could have been Beau's campaign.”