Seeking an edge on the national security issue, Republican presidential hopefuls on Saturday seized on the attack in Texas last week for which the Islamic State group claimed responsibility as an example of the threat they say the militant group poses to the United States.

"It's not a matter of if another attempt is made on American soil, it is when," Wisconsin Gov. Scott Walker said at a gathering of declared or potential contenders in South Carolina. "I want a leader who is willing to take the fight to them before they take the fight to us."

Two men were fatally shot last Sunday after opening fire with assault rifles at a heavily guarded exhibit of caricatures of the Prophet Muhammad in the Dallas suburb of Garland, Texas. The Syria- and Iraq-based Islamic State group claimed responsibility, but offered no proof. U.S. officials have said they doubted the militant group's direct involvement.