Hollis, New Hampshire (CNN) Hillary Clinton's new television ad slams Kevin McCarthy, the leading candidate to replace House Speaker John Boehner, for touting how the Benghazi committee's investigation has harmed her poll numbers.

The 30-second spot will air nationally on cable channels and highlights McCarthy's comment, as well as the $4.5 million the House panel investigating the deaths of four Americans in the 2012 Benghazi attacks.

It's the latest effort by Clinton's campaign to go on offense about an issue -- her exclusive use of a private email server during her tenure as secretary of state, which the Benghazi committee helped unearth -- that has dogged her campaign from its outset.

In a Fox News interview last week, McCarthy said: "Everybody thought Hillary Clinton was unbeatable right? But we put together a Benghazi special committee. A select committee. ... What are her numbers today?"

The Clinton ad's narrator says: "The Republicans have spent millions attacking Hillary because she's fighting for everything they oppose. From affordable health care to equal pay, she'll never stop fighting for you and the Republicans know it."

Clinton also made a passionate attack against Republicans herself on Monday, knocking the House Select Committee on Benghazi as "nothing but a partisan exercise," and saying if Democrats were doing something similar to Republicans, she would have shut it down.

"I would have never done that and if I were president and there were Republicans or Democrats thinking about that, I would have shut it down," she told NBC's "Today."

When asked by NBC's Savannah Guthrie if she would have made an issue out of the use of a personal email server had two high profile Republicans - Karl Rove or Dick Cheney - done the same thing, Clinton said angrily, "I would have never have done that. Look at the situation they chose to exploit to go after me for political reasons. The deaths of four Americans."

Last week, McCarthy ignited a backlash when he described how the committee had been effective at damaging Clinton's poll numbers. McCarthy has since walked back his comments

"I am sorry that I made a choice that has resulted in this kind of situation and I have said I made a mistake," Clinton said, before adding, "It is also, as we well know, it is the way the Republicans are trying to bring, as they admit, my poll numbers down."

Asked if the Benghazi committee should be disbanded, Clinton responded, "Now that they have admitted that it is a political partisan committee for the sole purpose of trying to go after me," but added that it is "up to the Congress" if they want to keep it going.

"If they are going to have it still running, I will be there," she said.

Republican spokesman for the committee Jamal Ware disputed Clinton's characterization Monday.

"Perhaps Secretary Clinton should at least do what the 50 other witnesses interviewed by this Committee, including survivors of the attacks, have done, and wait until she appears to make a judgment," he said in a statement.

Flanked by voters sitting at red checkered picnic tables and with pancakes sizzling in the background, Clinton used the more than an hour on NBC to cast herself as the most prepared candidate in the 2016 field and subtly knock Bernie Sanders, her stoutest opponent for the Democratic nomination.

Clinton aides rolled out the candidate's plan to combat gun violence on Monday morning, pledging to close background check loopholes and allow victims to sue gun manufacturers.

During the town hall, Clinton said she wanted "to push hard to get more sensible restrains on gun ownership in the wrong hands and then try to keep track of people who shouldn't have guns."

"If anything else were killing 33,000 of our people, we would come together and say 'hey, what are we going to do about this,'" Clinton said.

Clinton also previewed how she may go after Sanders on college affordability, an issue she has knocked the Vermont independent on before.

Clinton's plans would promises that students would not have to "borrow to pay for tuition, books and fees to attend a 4-year public college in their state. Sanders, on the other hand, has pledged totally tuition free public college and universities.

"I am a little different than those who say free for everybody," Clinton said, not mentioning Sanders by name. "I am not in favor of making college free for Donald Trump's kids."

Sanders' message has been resonating in New Hampshire, though, and the new state of play in the state is Sanders in the lead and Clinton in second.

"I have got work to do in New Hampshire," Clinton said bluntly, before noting that she leads in Iowa, South Carolina, Nevada and nationally.

Asked if she was surprised by the rise of Sanders, the former secretary of state bluntly said "no."

"I really believe this is great for the Democratic Party and for this election," she said. "We want to turn out as many people as possible in order to understand and believe what we both believe."

Republican front-runner Donald Trump is also expected to talk at a "Today" town hall in the coming weeks, but a date has not been announced yet.