BOSTON -- Hillary Clinton warned Sunday that Donald Trump's latest attacks about the controversies of her husband's past are a "dead end" that "won’t work."

"It's been fair game going back to the Republicans for some years," Clinton said.

"They can do it again if they want to. That can be their choice as to how to run in this campaign. Didn't work before. It won't work again," she added. "I'm going to talk about the differences between us because I think that's what Americans care about."

Earlier this week, Republican frontrunner Donald Trump released an ad featuring former President Bill Clinton and Monica Lewinsky.

Clinton, who has said it's her "New Year's resolution" not to engage with Trump, attempted to brush off the ad on Sunday.

"Well, it he wants to engage in personal attacks from the past, that's his prerogative. You know, so be it," she said. "He can say whatever he wants to about me, but I am not going to let him, or any of the other Republicans rip away the progress have made. ... I'm going to stand up and make it clear there is a huge difference between us."

The interview on Sunday came the same morning a new NBC/Wall Street Journal/Marist poll was released showing Clinton and Vermont Sen. Bernie Sanders virtually neck-in-neck in Iowa.

Clinton, however, didn't seem fazed.

"These polls go up, they go down," she said. "I stay pretty focused, as I think we all should, on what we have to do to build on the progress of the Obama administration, but go even further."

Later today, Clinton will receive the official endorsement from the Planned Parenthood Action Fund at a campaign event in New Hampshire –- a state where she is also in a heated race with her Democratic challenger.