Editor's note: Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author of "Jimmy Carter" (Times Books) and of the new book "Governing America" (Princeton University Press).
Princeton, New Jersey (CNN) -- As Republicans struggle to make a decision in this primary season and President Obama appears to gain ground, the party has been flailing around, trying to find the right issues on which to base its campaign.
Republicans seem to be pulling back a bit from the social issues that raised red flags about extremism and irrelevancy.
During the build up to Super Tuesday, Republican presidential candidates other than Ron Paul turned to another classic campaign theme — national security. Responding to Israeli Prime Minister Benjamin Netanyahu's visit to the United States, the candidates castigated President Obama, saying he was being too timid about Iran and promising that if elected, they would be willing to use force against Iran.
The Republicans have also assured voters that they would never apologize for U.S. actions, as the president did to the Afghan government following the burning of a Koran by some U.S. soldiers. Mitt Romney warned that, "if Barack Obama gets re-elected, Iran will have a nuclear weapon" while Newt Gingrich said that, with Iran, the United States was "being played for fools."
The only exception has come with Afghanistan, where some of the Republicans have criticized Obama for being too hawkish in the wrong place. Following the attack on Afghan civilians by a U.S. soldier this weekend, Gingrich admitted that "It's very likely that we have lost, tragically lost the lives and suffered injuries to a considerable number of young Americans on a mission that we're going to discover is not doable."
The fact that the GOP is trying to bring its "tougher on defense" argument into the campaign is not a surprise. This has been a traditional theme for the Republican Party ever since the end of World War II when conservatives in the party argued that President Harry Truman was not tough enough against the Soviet Union, and then claimed in 1949 that he allowed China to fall to communism.
In good times and bad times, Republicans have continued to use this argument to undercut the political strength of Democrats. At certain moments such as the election of 1952, when Dwight Eisenhower defeated Adlai Stevenson or in 2004, when President George W. Bush defeated Senator John Kerry, national security has worked as an issue for the GOP.
But barring some bigger national security crisis flaring before the election in November, this time the strategy won't work. The polls have been quite clear that voters are primarily concerned about the economy. Even with signs of recovery, the severity of the current recession makes economic security the theme of our times.
According to The New York Times, in every state on Super Tuesday voters told pollsters that the economy was the major factor behind their choice of candidate. The situation is not unlike 1992, when a recession drowned out interest in foreign policy and thus undermined the ability of the incumbent, President George H.W. Bush, to use his success in Operation Desert Storm as a way to defeat then-Gov. Bill Clinton. As James Carville's slogan said, "It's the economy, stupid."
The condition of the economy is not the only reason, however, that Republicans will have trouble using national security as a winning issue. There has been a subtle shift in the politics of national security under President Obama, one that has built on some of the political advances that had been made by Democrats when President Clinton was in the White House.
Like Clinton, President Obama has made a series of moves that have dampened the ability of the GOP to brand their opponents as weak on defense.
He's maintained an aggressive stance in the war on terrorism. Although Obama's campaign in 2008 revolved around his opposition to the war in Iraq and willingness to question the tactics used in the war on terrorism, the president has repeatedly shown that he is no dove.
He has authorized the use of drones against al-Qaeda that has helped to severely weaken the structure of the network. The president agreed to the use of air strikes against Libya that helped bring down the government .
Although he has curbed some of the executive action taken under President George W. Bush, in other areas he has expanded what the government can do. The authorization for the "targeted killing" of American citizens overseas, for instance, has been one of the most striking examples of where President Obama seems even tougher than President Bush.
Another key factor is the aftermath of the war in Iraq, a war that weakened the Republican advantage on national security and raised questions about the competence of the GOP on foreign affairs. The cost of the war and its messy consequences challenges the public's confidence in this kind of military operation against rogue states.
Given that the war started under a Republican president, the GOP will not be able to easily shake the public's memory of how the unpopular and controversial mission began.
Just as Democrats were saddled with the responsibility for putting American into a quagmire with the Vietnam War, Republicans have seen their brand tarnished by the Iraq experience. It overshadows the memory of the party under Ronald Reagan, whose strong stance against the Soviet Union was given credit by many Americans for ending the Cold War.
The final factor against this Republican strategy is the nature of the international threats that we face now. In the days of the Cold War, American voters were always concerned with the potential for a nuclear attack from a fully armed adversary. After 9/11, fears about another terrorist attack loomed large in the public psyche.
The debate over Iran is about the potential threat from a rogue state in a distant region while the crises in countries like Syria don't pose a clear and immediate threat to America.
Following his victories on Super Tuesday, Mitt Romney seemed to get the message about the weakness of the national security theme as he shifted his focus back to economics.
If the GOP invests its campaign capital on national security, the chances are it will go down to defeat.
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The opinions expressed in this commentary are solely those of Julian Zelizer.