When Iowans sat down to watch television over Thanksgiving weekend, they glimpsed the usual ads for Black Friday sales, car dealerships, and conservative talk shows. Interspersed between these, however, were some of the first political attack ads of the 2016 cycle. It was the official commencement of hostilities between the two candidates increasingly seen as the front-runners to challenge Donald Trump for the Republican nomination.

American Encore, a group with connections to Marco Rubio, released its first attack ad the Monday before Thanksgiving hammering Ted Cruz for “weakening national security” by supporting the USA Freedom Act in Congress. Cruz pushed back a few days later, circulating his own television spot that emphasized his commitment to an assertive foreign policy and hit his Florida foe in his weakest spot: immigration. The ad touted the way Cruz had “stood up to both Obama and Marco Rubio when they joined forces to provide amnesty without border security.” In November, a PAC backing Cruz also ran radio ads that suggested that Rubio is nothing more than a pretty face.

Rubio has since ramped up his attacks on Cruz in speeches and interviews. In mid-November, he tried to link Cruz to liberal stalwarts like Senator Chuck Schumer and the American Civil Liberties Union, saying that they worked together “to harm our intelligence programs,” again citing Cruz’s support for modest limits on surveillance programs contained in the USA Freedom Act. Rubio recently told a conservative talk show that Cruz “voted to weaken our intelligence programs at a time when intelligence is a critical component in the war on terror,” according to the The New York Times. Though Rubio is vulnerable on immigration, he has nonetheless tried to hammer Cruz on that issue as well, noting in November that the Texan senator supports “a massive expansion” of work visas for foreigners with college degrees.

A slugfest between Rubio and Cruz may be inevitable. Both conservative senators were sent to Washington by Tea Party insurgencies, and they are increasingly seen as the best hope to wrest the nomination from Donald Trump. But could their crossfire prove a form of mutually assured destruction? Or will Cruz, whose attacks have so far shown more surgical precision—and who has more red meat to feed the base—be positioned to capture Rubio voters?

The last time two candidates went to war in Iowa in an open, multicandidate presidential primary was during the bloody Democratic battle in 2004 between former House Majority Leader Richard Gephardt and former Vermont Governor Howard Dean. Starting around Thanksgiving the previous year, with eight candidates in the mix, Gephardt and Dean, the Iowa frontrunners, took aim at each other on the airwaves. Only two years after September 11, with the Iraq War raging, foreign policy was the issue stirring up the Democratic base. Dean and Gephardt attempted to undermine each other’s credibility on national security. The negativity soured voters on both candidates, sending their supporters to Senator John Edwards of North Carolina, who finished an unexpectedly strong second in Iowa, and Senator John Kerry, whose Iowa comeback propelled him to the nomination.

“You could be a good campaign with a really good message, and some other idiot in the race has a strategy that may or may not any strategic sense. But guess what? You are in a multicandidate race,” says Joe Trippi, the Democratic strategist whose advice propelled Dean from dark horse to early 2004 frontrunner. “You now have to make a series of bad decisions that you would never ordinarily make.”

In late November of 2003, with the former Vermont governor his biggest impediment in Iowa, Gephardt embarked on an increasingly personal campaign to tarnish Dean. A group with ties to the Gephardt campaign released its harshest ad in December. “Howard Dean just cannot compete with George Bush on foreign policy,” the narrator says, while a magazine cover featuring Osama bin Laden’s face flashes on screen. “It’s time for Democrats to think about that, and think about it now.”

Dean was forced to respond, releasing his own attack ads in Iowa that pummeled Gephardt for supporting the Iraq War. One spot included images of Gephardt and President Bush in the Rose Garden after Congress passed a resolution allowing the president to use force against Saddam Hussein. It was, Dean campaign operative Roy Neel later told CNN, “one of the most negative campaigns I have ever seen.”

But with his favorability ratings plummeting, Dean decided to release yet another ad hammering not only Gephardt, but also Kerry and Edwards for supporting the Iraq War. Gephardt hit back with a somewhat spurious ad critiquing Dean’s stances on Medicare and Social Security. Dean pollster Paul Maslin would later write that that last exchange “sent us hurtling to a crushing defeat instead of a narrow loss that we should have been able to endure,” with both Gephardt and Dean “increasingly seen by Iowans as running negative campaigns.”

Trippi says, “The facts are that when two candidates go at it in a multicandidate race, you might succeed in knocking votes off the candidate you are hitting, but it is very rare that they would go to you.”

Political scientists agree. “In primary elections, attacking someone of your own party does hurt you,” says Patrick Meirick, an associate professor in the Department of Communication at the University of Oklahoma, where he studies the influence of political advertising. This is the rationale, he says, behind Ronald Reagan’s oft-cited eleventh commandment: “You shall not speak ill of a fellow Republican.” 

The 2004 primary demonstrated that principle on the other side of the aisle. Dean and Gephardt finished third and fourth—disastrous results after being Iowa favorites. Dean limped into irrelevance, and Gephardt formally dropped out a day after the caucuses. “It was murder-suicide,” says Trippi. “He killed us knowing that he was going to kill himself.” Gephardt did not immediately respond to requests for comment from the New Republic.

By one measure, at least, the Republicans’ presidential sweepstakes in 2016 looks like the Democrats’ 12 years ago: It’s utterly impossible to predict who might prevail. The 2004 cycle was the last time we saw a sprawling field of candidates that, less than two months before Iowa, still included at least half-a-dozen plausible contenders for the nomination. But according to Trippi and some political scientists, the similarities may end there. By dint of superior strategy—and a greater arsenal of conservative critiques to lob at Rubio—Cruz might be positioned to emerge the winner from this battle in a way that neither Dean nor Gephardt could.  

Cruz’s rationale for attacking first was clear. “While Cruz is certainly disliked by much of the party, he believes that he has the evangelical community behind him and that he can make enough inroads with some more moderate types to be successful,” says Martin Cohen, an associate professor of political science at James Madison University. “He sees Rubio as the establishment threat, the one that is in his way, and he is therefore knocking him down.” 

“Why Cruz is doing this makes tremendous sense,” Trippi says. “You know the strength of the evangelical Christians from Santorum and Huckabee [and their victories in Iowa in 2012 and 2008, respectively]. You let Carson corral them. You say sweet things about Donald Trump. You want to be there to pick up the pieces when Carson inevitably fades. But there is one other guy you have to get out of the way, and his name is Marco Rubio.”

Cruz has a leg up on Rubio: ammunition. Labeling Rubio an establishment figure—one who supported amnesty and who worked with the Gang of Eight on immigration reform—could be very effective in the current political climate, in which many Republicans think that their representatives in Washington have sold them out. Cruz has adhered to those talking points religiously. 

For months, Rubio avoided rebutting those charges, perhaps attempting to skirt the risky crossfire that took down Dean. But as Cruz continued to attack, Rubio, like Dean, had to respond. “Cruz is still coming at you,” Trippi says. “Are you just going to sit there while the other guy wraps an anchor around your ankles and throws it over the side of the boat? No, you’re going to grab the anchor and hit him over the head.”

However, it may be harder for Rubio to land punches that both hurt Cruz and elevate his own support. “If Rubio attacks Cruz, the voters who move away from Cruz don’t have to go to Rubio,” says Stephen Ansolabehere, a Harvard professor who coauthored a seminal book on negative advertising, Going Negative. “They could just as well go to Trump or Carson or someone else. Rubio’s attacks in that case might very well make him worse off by raising the support of other competitors.”

The negativity could theoretically drive Rubio’s supporters towards another dark horse candidate, Chris Christie, or even Trump. Rubio’s choice to hammer Cruz on foreign policy, specifically, may even make things worse for him. Even if Rubio succeeds in making Cruz seem soft on national security, voters might be more likely to decamp to Trump or Christie, two candidates who have framed themselves as tough guys on foreign policy.

Rubio also seems to be struggling to hit Cruz back in a damaging way. Despite being hammered for days, the Texas senator is still gaining in Iowa: the most recent polls have Cruz leading the pack for the first time with 24 percent support, up three points in the last three weeks. Furthermore, while Democrats thought the battle between Gephardt and Dean made both seem ungentlemanly and unpresidential, the Republicans who support Cruz seem to like his incendiary style. 

Rubio, on the other hand, has more to lose. If he continues to attack Cruz—moving further away from the inspirational, American Dream rhetoric he has thus far employed—his more sedate, establishment supporters could penalize him for it. That, in turn, could make it tougher for Rubio to build the momentum he needs to keep Cruz from locking up too many of the voters he still hopes to win over. Unless Cruz has more vulnerabilities on the right than Rubio’s opposition researchers have been able to find so far, he very well could be the one to benefit from a battle with Rubio.