Nothing will matter more than attacks — and surviving them — in the final 15 days before voters drop the hammer in Iowa and lock in the trajectory for the White House, political strategists say.

With the Democratic and Republican presidential races in Iowa neck and neck, the campaigns are in all-out warfare mode. Rivals are no longer delicately insinuating insults and instead are drilling into their rivals by name.

The big questions now are: Which attacks will hit the bloodstream and jolt voter opinions? Which ones will fall flat?

And can anyone withstand the armor-plated assault force that is Donald Trump if he wins both the Christian conservative-leaning Iowa caucus and the more secular New Hampshire primary, a feat never achieved in modern GOP presidential history?

In Iowa, an amazing ground game — a one-on-one effort to persuade voters to show up on Feb. 1 — can gain points in the final tally. But an attack played just right can siphon away far more, strategists said.

“Bernie (Sanders) may be able to close the sale with Iowa libs,” said Doug Watts, a longtime GOP strategist who formerly worked for Ben Carson’s presidential campaign. “As for Republicans, I’m sorry, but Trump never disappoints.”

The attack lines to watch out for will be those directed at poll leaders Hillary Clinton, Sanders, Ted Cruz, Trump and also Marco Rubio, operatives said. Rubio, despite being a distant third in the GOP race, has the potential of a double-digit leap because of his shiny favorability rating: 73% of likely Republican caucusgoers have a positive opinion of the Florida U.S. senator, edged by Cruz at 76% but well ahead of Trump’s 54%.

Most of the other squabbles, strategists said, will likely be seen as cries of campaigns long gone in Iowa.

In the Democratic race, Sanders, a 74-year-old Vermont U.S. senator and liberal revolutionary, is just 2 percentage points down from establishment favorite Clinton, a 68-year-old former U.S. secretary of state, the new Des Moines Register/Bloomberg Politics Iowa Poll shows. On the Republican side, Trump, a 69-year-old New York businessman, is just 3 points down from fellow conservative pepper pot Cruz, a 45-year-old Texas U.S. senator.

As presidential street fighters feel their poll numbers wobble, could Iowa start to resemble the fight scene from Anchorman? In the cult classic comedy, rival news teams battling for television ratings engage in a back-alley brawl that turns grisly. “Boy,” the lead character says, “that escalated quickly.”

Clinton now on attack; Sanders fighting back

Clinton has carefully protected a lead throughout the race, but at the one-month-out point, she had to get less cautious fast, and Sanders is fighting back in his big, booming voice, Democratic strategists said.

“It already has gone from zero to 40 pretty quickly. Sunday’s debate and the media traffic these next few days will offer a clue as to how torqued it might get,” said Democratic strategist David Axelrod, referring to the debate at 9 p.m. ET Sunday in South Carolina, the final Democratic debate before Iowa votes.

Bumper cars aren’t as chaotic with only two cars — three if you count former Maryland Gov. Martin O’Malley, who has almost no gas — but the Democratic race is expected to be no less intense than the 11-person GOP fight club.

Like in 2008, Clinton faces the specter of having the rug pulled out from underneath her after months as presumptive winner. She has declined since an early December Iowa Poll with some of the groups she was most popular with: seniors, those in the highest income group and those with their minds made up, noted J. Ann Selzer, pollster for the Iowa Poll.

Democratic upstart Barack Obama won the 2008 Iowa caucuses by gathering an army of younger voters, independent voters and first-time caucusgoers, according to entrance polling.

Sanders has a much bigger lead now with this collection than Obama did in the final pre-caucus poll in the 2008 cycle, Selzer said. The coalition made up 76% of caucusgoers eight years ago, and Obama led with 36% to Clinton’s 23%. Now, it’s 57% of the electorate, and Sanders leads Clinton 53% to 31%.

“It wouldn’t take much to build on that foundation,” Selzer said.

But Clinton remains very popular, the Iowa Poll shows.

Among likely Democratic caucusgoers, 86% have a favorable opinion about her; just 12% don’t. Among those who backed Obama in 2008, it’s 90% favorable, 7% unfavorable.

Very few, just 5%, have a “very unfavorable” opinion of her, which is akin to hate, Selzer said.

For now, Clinton is attacking Sanders for straying from his progressive roots on various issues, including gun control, but a better attack might be to ask how he can start a revolution if he can’t get a bill passed after 25 years in Washington, strategists said.

“The truer critique is that his proposals, however well-meaning, are unlikely to happen, so a vote for Bernie is more symbolic statement than a prelude to action,” Axelrod said.

For Sanders, “his sharpest attack is that Hillary is too mortgaged and malleable to be a true agent of change,” Axelrod said.

Trump gets advantage by striking first

In a cycle when paid television advertising has proved less effective so far, candidates are competing for free air time in the news. Trump, the king of TV, has shown that the best way to get coverage is to be provocative and engage another candidate in fisticuffs, said Syracuse University’s Robert Thompson, an expert on television and pop culture.

His rivals are now doing the same.

“When you corner an animal and it has no way out, generally it’s more likely to attack then roll over and show you its tummy,” Thompson said. “Those attack messages are more likely to get covered, and they’re also more likely to get people to start shouting, ‘Amen!’ ”

The reason attacks work is that they’re sticky.

Except, it seems, when it comes to Trump, the TV celebrity, Thompson said. Traditionally, if a candidate wanted to craft a deadly attack, he’d accuse his rival of believing in his heart certain negative things about women, immigrants, Muslims and disabled people, Thompson said.

“Trump beats you to it,” he said.

But how does Trump get away with it, without alienating his fans?

“His secret is that he is the exact antithesis of the politician they hate most, and that allows him to do absolutely anything,” said Frank Luntz, a focus group pollster closely following the 2016 race.

Luntz explained: Obama is teleprompted; Trump is off the cuff. Obama is calm; Trump is wildly in your face. Obama has a clearly defined ideology; Trump picks and chooses. Obama avoids the concept of American exceptionalism; Trump wraps himself in the flag. Obama is discipline; Trump is spontaneity. Obama is status quo; Trump is radical change.

The notion that if Trump wins Iowa on Feb. 1, he can’t be defeated — even in the general election in November — exasperates Liz Mair, strategist for the anti-Trump super PAC Make America Awesome.

“It’s inaccurate to say that attacks don’t stick to Trump,” Mair said. “Barely a feather has really been laid on Trump.”

The secret to his demise, she said, is to expose the record of how he has treated employees.

“The truth is, Trump is just another rich guy who has gotten wealthier off the backs of average Americans just like the ones he’s appealing to now, whether they’ve worked for him or they’re taxpayers, and the policy he’s advocating will make average Americans even worse off,” Mair said.

Attacks gain traction with news coverage

But Trump is an attack genius, strategists said.

When The Des Moines Register asked more than a dozen political operatives which attack has been most devastating this presidential election cycle, almost all of them named Trump’s two-word attack on Jeb Bush, the GOP’s early national front-runner: “Low energy.”

That four-syllable insult cast doubt on Bush’s energy and strength, and demolished $100 million of “shock and awe” fundraising, they said.

“No question that is the most memorable and effective attack on the Republican side,” Watts said.

It remains to be seen whether Trump’s big new attack on Cruz — that it might be unconstitutional to elect someone born in a foreign country — will penetrate as much. Cruz is adamant that his Canadian birth to an American citizen mother makes him a “natural born citizen” as the Constitution requires.

So far, it doesn’t bother 83% of likely GOP caucusgoers that Cruz was born outside the United States, the Jan. 7-10 Iowa Poll shows. Fifteen percent are bothered.

But Trump’s attack has been a top political news story for a week now, and a lawsuit was filed Thursday in Texas.

“This is a potential train wreck. Even if it has no merit,” said Iowa politics watcher Steffen Schmidt, a professor at Iowa State University.

The vehicle has a lot to do with the effectiveness of an attack, because news coverage is what gives an attack enough repetition for it to become memorable, said GOP strategist Tim Saler.

This election cycle, only Trump can drive that kind of coverage, Saler said. A clever messenger like New Jersey Gov. Chris Christie, who sits at 3% in Iowa, could attack as ferociously as Trump attacks, he said. But without the repetition of news coverage, the attack likely won’t be anywhere near as effective.