WASHINGTON (CNN) -- When it comes to campaign commercials, Sens. Barack Obama and Hillary Clinton are going where no candidate has gone before.
A Clinton ad on the economy mirrors a spot that aired in March.
"Obama and Clinton have spent a combined $110 million on TV ads to this point; we've had a race that's literally gone on since last summer for ad spending," said Evan Tracey of TNS Media Intelligence/Campaign Media Analysis Group, CNN's consultants on campaign commercials.
"We're beyond what has been record spending in previous presidential nomination campaigns. John Kerry spent close to $20 million to get the nomination four years ago. Barack Obama's already approaching $70 million."
Obama outspent Clinton on ad buys in Pennsylvania by slightly more than 2-to-1, and Tracey says Obama is outspending his rival for the Democratic presidential nomination by about the same ratio in Indiana and North Carolina, which hold primaries May 6. Watch more on the Democratic race »
But is Obama getting bang for the buck?
Clinton "has been able to dictate the tempo in the last few contests, be that Texas, Ohio and then Pennsylvania," Tracey said. "What she has to continue to do is dictate the tempo of this race with her TV ads. She doesn't have as much money ... but if she's allowed to dictate the tempo, she can make up for that lack of spending."
An example of that is Clinton's "3 a.m." commercial, which asked, "It's 3 a.m., and your children are safe and asleep. Who do you want answering the phone?"
The commercial touted what the Clinton campaign calls its candidate's experience advantage over her rival.
"Clinton used the 3 a.m. ad very effectively to put the Obama campaign back on their heels. She did it again in Pennsylvania," Tracey said. Watch one of Clinton's "3 a.m." ads »
Another commercial summoned a phrase associated with a former Democratic president: "Harry Truman said it best: If you can't take the heat, get out of the kitchen. Who do you think has what it takes? I'm Hillary Clinton, and I approve this message."
The ad again touts Clinton's experience and questions Obama's strength and resolve, without mentioning him by name.
The ads have forced Obama to respond.
His campaign quickly put out its own "3 a.m." ad criticizing Clinton's vote on the Iraq war and also went with a commercial in Pennsylvania with this counterattack: "Newspapers call Hillary Clinton's negative attacks the old politics."
"What she's been able to do with some of these ads that attack Sen. Obama is basically make him into a political candidate," Tracey said. "That's the problem Obama's trying to avoid. Obama right now, he's got to decide: Does he take the fight to Clinton? In other words, does he strike first?"
Obama fundraising machine has built an advantage in money to buy ads, but Clinton's win in Pennsylvania could help close the gap.
"Hillary Clinton's victory in Pennsylvania was extremely important. It has given her that boost in momentum that she needs going into Indiana and North Carolina, and it has helped her fundraising tremendously at a time when she's at a severe disadvantage to Barack Obama," CNN Political Editor Mark Preston said.
Republican Sen. John McCain has spent just less than $10 million on ads. He has the luxury of already having sewn up his party's nomination while the Democrats continue to battle. Watch more on McCain's campaign »
But he trails both candidates when it comes to raising campaign cash, and while the Clinton-Obama nomination fight stays in the spotlight, McCain is having a tough time staying in the headlines. Can campaign commercials help him?
"John McCain, ad-wise, has been doing a few tactical ads. He ran a few ads late in Pennsylvania, in the Pittsburgh market," Tracey said. "McCain runs the risk of being covered by a campaign that starts with 'and in other news.' And he's going to do what he can to keep in the news. Getting ads out there is one way that he's been able to do that." E-mail to a friend