On WMUR, the dominant television station in Manchester, N.H., about 25 percent of commercial time is being eaten up by presidential campaign ads. Already this week, the candidates and their allies have fired off a dozen new commercials, a third of them negative, in Iowa and New Hampshire markets.

The “super PAC” supporting Senator Marco Rubio of Florida unleashed multiple advertisementsblasting Gov. Chris Christie of New Jersey and his record. The super PAC backing Senator Ted Cruz of Texas portrayed Mr. Rubio as unfit for the presidency. And the outside group supporting Jeb Bush ripped into Mr. Rubio’s Senate attendance record in one ad and favorably contrasted Mr. Bush’s accomplishments with those of Mr. Christie and Gov. John Kasich of Ohio in another.

The ad wars of the 2016 election are at hand.

“We’re getting down to the firing-squad part of the campaign,” said Larry McCarthy, the strategist making ads for Right to Rise, the super PAC supporting Mr. Bush. “It’s like the end of the Quentin Tarantino movie, where everyone is shooting everyone else.”

It is also a huge bet that television advertisements will remain a crucial, even decisive, political battlefield when signs increasingly suggest otherwise. Candidates and their allies spent nearly $100 million on political advertising last year, including $72 million in Iowa and New Hampshire alone, Kantar Media/CMAG estimated. Much of that was spent by candidates promoting themselves, not attacking their rivals. Yet the biggest spenders reaped only scant improvement in the polls.

Now, with three and a half weeks until the Iowa caucuses, presidential campaigns that spent much of 2015 wooing donors and amassing large amounts of money are spending that money hand over fist, feverishly vying to buy time during every popular show from morning to late-night TV. From Sunday to Thursday alone, according to Kantar, candidates and their allies in both parties spent an estimated $5.9 million on television ads — roughly a third of what was spent in the 2012 Republican race from the beginning of 2011 through the Iowa caucuses. And much more of it now is going toward attempts to take down their rivals.

Turning nasty has grave risks, though, perhaps even more so this cycle, given the more than a dozen candidates in both parties fighting for airtime and attention.

“If you attack somebody else, their support leaves, but it doesn’t necessarily move to you,” said Tad Devine, the longtime Democratic strategist overseeing ad creation for Senator Bernie Sanders of Vermont. “It can be a very dangerous maneuver.”

Few campaigns dared to risk that blowback effect in 2015, though there was another reason to shy from mudslinging: The likeliest target of negative ads, the front-runner, was Donald J. Trump, who showed himself more than willing to go after those who provoked him, often in humiliating terms.

Even now, few Republicans have directly attacked Mr. Trump in television ads. Mr. Bush and Mr. Kasich, the most prominent exceptions, have little to lose, given their standing in the polls.

Yet it is Mr. Trump, with his ability to generate perhaps hundreds of millions of dollars of free television time in the form of news coverage, to whom many political ad makers attribute the growing doubts about the power of political advertising.

For one thing, the shock value of the average blunt, starkly graphic television commercial is diminished when the news show it interrupts covers an even more shocking pronouncement.

“Television ads run on TV, and Donald Trump is a TV phenomenon,” said Fred Davis, the Republican strategist making ads for New Day for America, the super PAC supporting Mr. Kasich. “He would say things that were so much more outrageous than what anyone would ever put in a paid ad.”

Mr. Trump’s presence has also generated previously unheard-of ratings for the Republican presidential debates, turning political coverage into must-see television and giving people who might have been loosely familiar with the campaign a real-time feel for it. As a result, commercials that once offered a prime tool for candidates to inform and persuade are proving less useful at either.

“Ads might be playing a lot less dominant role than they had in the past, partly because more people are getting their info from debates,” said Mr. McCarthy, of Right to Rise.

It has not helped that the crowded field of candidates has been saying many of the same things.

In New Hampshire, Right to Rise, New Day for America and America Leads, the super PAC supporting Mr. Christie, combined to spend an estimated $26.4 million in 2015, more than two-thirds of the total spent on television by all Republican candidates and their allies in the state, according to Kantar. Each produced at least one ad focused on terrorism, with fearsome shots of Islamic State terrorists.

“You have to do stuff that others aren’t doing at the same time,” said Mr. Davis, of New Day for America. “The ones that are the most effective are when everyone is doing ISIS and you switch to Trump’s a hippopotamus,” he added, referring to his group’s advertisement likening Mr. Trump to the large mammal.

Read the original story at The New York Times.

WASHINGTON, Nov. 14 — Frustrated with the slow progress of legislation in Washington on energy and global warming, the nation’s governors have created regional agreements to cap greenhouse gases and are engaged in a concerted lobbying effort to prod Congress to act.

Beginning Monday, three Western governors will appear in a nationwide television advertising campaign sponsored by an environmental group trying to generate public and political support for climate change legislation now before the Senate.

The 30-second ad features Arnold Schwarzenegger, Republican of California; Jon Huntsman Jr., Republican of Utah; and Brian Schweitzer, Democrat of Montana, standing in casual clothes in scenic spots talking about the threat posed by greenhouse gas emissions. The nation’s governors are acting, but Congress is not, they say. “Now it’s their turn,” Mr. Schwarzenegger says.

Separately, in Milwaukee on Wednesday, nine Midwestern governors and the premier of Manitoba signed an agreement to reduce carbon emissions and set up a trading system to meet the reduction targets. The Midwestern accord is modeled on similar regional carbon-reduction and energy-saving arrangements among Northeastern, Southwestern and West Coast states.

The advertising campaign is underwritten by Environmental Defense, an advocacy group that is pressing for quick action on a climate change proposal sponsored by Senators Joseph I. Lieberman, an independent from Connecticut, and John W. Warner, Republican of Virginia.

The Lieberman-Warner legislation would cap carbon emissions at 15 percent below 2005 levels by 2020 and set up a system for polluting industries to trade emissions credits to meet the goals. Like other such bills before Congress, it would provide incentives for research on capturing and storing carbon dioxide from power plants and subsidies to help the poor handle the higher costs of electricity in a carbon-constrained economy.

The bill is now before the Senate Environment and Public Works Committee. The committee’s chairwoman, Senator Barbara Boxer, Democrat of California, said she hoped to bring the bill to a vote of the full committee by Dec. 6. There is no schedule for action after that, however.

The governors, who did not receive a fee for appearing in the advertisement, say state leaders are moving to reduce climate-affecting emissions, while the current Congress has so far failed to pass any significant legislation on climate change or energy.

“In state after state, we’re taking action,” the governors say, taking turns speaking. “Now it’s time for Congress to act by capping greenhouse gas pollution.”

In an interview, Governor Huntsman said, “With just weeks left in the legislative calendar, there has been no vote yet dealing realistically with greenhouse gas pollution. We in the West are already wrestling with it and setting ambitious targets.”

He said action on the national level, in the form of the Lieberman-Warner legislation or a similar economywide carbon cap-and-trade scheme, was preferable to the patchwork system that state governments were putting in place.

Governor Schweitzer said dealing with global warming was the “greatest imperative” of this and future generations. “We need to find a sustainable, renewable American energy supply so we will not commit the next generation to fight another oil war,” he said.

Mr. Schweitzer added: “Here’s a novel concept for Congress. Do something. Anything. Move.”

Environmental Defense is spending $3 million to broadcast the advertisement, which will appear in 17 markets in 11 states over the next few weeks, said the group’s president, Fred Krupp. The ad will also appear during the Sunday morning talk shows on Nov. 25.

The Midwestern governors expressed similar impatience with the slow pace in Washington on global warming and energy issues. They have banded together to set up a regional emissions control program, to expand production of biofuels and to cooperate on environmental and energy infrastructure projects, like an interstate pipeline for moving carbon emissions from power plants to underground storage vaults.

Gov. James E. Doyle of Wisconsin, a Democrat who is chairman of the Midwestern Governors Association, said that the individual states in his region were all moving independently toward greater energy efficiency and planned to reduce greenhouse gas emissions, and that it made sense to work in concert.

“In the absence of a federal plan we have to move forward,” Mr. Doyle said, speaking from Milwaukee, where he was the chairman of an energy summit meeting of the Midwestern governors. “On top of that, this recognizes that, federal plan or no federal plan, the Midwest is uniquely positioned to be a major force in the developing new energy world.”

He predicted that sooner or later Washington would adopt a national cap-and-trade system for carbon emissions, but he was not optimistic that it would act before President Bush leaves office.

“I suspect it will require a new administration to come in,” he said. “There’s a lot of work to be done to prepare for it. If there comes a national cap-and-trade system, we will have done a lot of the work. If not, we will have one in the Midwestern region on a scale that can work.”