The gunfire and explosions in Paris will likely move national security issues to center stage in a Democratic primary that has so far largely focused on progressive issues such as income inequality and controversies like Hillary Clinton's use of private email during her tenure as secretary of state.

Barack Obama calls Paris massacre 'outrageous'

Clinton's views on foreign policy, honed during her time as the Obama administration's top diplomat, could play a large role in the debate, which will start at 9 pm ET. The relative inexperience of her rivals -- Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley -- on the world stage could also be on display.

CBS, which is hosting Saturday's debate, informed the Democratic candidates that the format would be changed to incorporate questions about the Paris attacks at the the start, a shift met with some resistance from the Sanders campaign.

According to a source on a call between debate organizers and the campaigns, a Sanders aide "completely lost it" when informed of the change and argued that it shouldn't be allowed. After the rift was reported by Yahoo News, Sanders campaign manager Jeff Weaver denied the dispute was resistance to discussing the attacks themselves, saying the conflict revolved around a push to shorten opening statements in order to accommodate for time to talk about the attacks.

"They wanted to make some last minute changes to the debate, we obviously wanted to keep the format to what had been agreed to, and I think people on our staff argued vigorously to that and were successful," Weaver said.

2016 hopefuls express shock, condolences for Paris attacks

The horrific events of Friday, for which ISIS has claimed responsibility, have quickly penetrated the American political world. White House candidates from both parties have reacted to the Paris attacks, offering a mix of condolences and national security policy prescriptions.