President George W. Bush visited a Muslim mosque six days after the terror attacks of Sept. 11, 2001, to remind Americans that "Islam is peace." Discussing terrorism at the fifth Republican presidential debate, his brother, Jeb Bush, said Tuesday evening that the country needs to follow the former president's lead in the fight against Islamic extremism.

"We can't dissociate ourselves from peace-loving Muslims," Bush said. "If we expect to do this on our own, we will fail."

The former Florida governor also called for the United States to embed troops in the Iraqi military and create a safe zone for refugees in Syria.

He also said the U.S. needed to "have a military that is second to none." "The main thing we should be focused on is how to keep us safe," Bush said. "It requires leadership."

Throughout the debate, Bush and businessman Donald Trump traded insults -- a spat that started with the former governor calling Trump a "chaos candidate." 

"He has totally failed in his campaign," Trump said, dismissing Bush's remarks. "It has been a total disaster. Nobody cares."

Bush was once considered a strong contender for the 2016 Republican nomination, but he has been sinking in the polls since June, narrowly qualifying for Tuesday's prime-time stage. In the latest ABC News/Washington Post poll, Bush received only 4 percent of support from GOP primary voters. Candidates needed an average of 3.5 percent nationally in polls conducted Oct. 29-Dec. 13 to make the cut.

Trump was featured front-and-center of the debate stage because he leads in the polls. Neurosurgeon Ben Carson, Texas Sen. Ted Cruz, Florida Sen. Marco Rubio, former Hewlett-Packard CEO Carly Fiorina, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich, and Kentucky Sen. Rand Paul also joined Bush and Trump on the main debate stage.

The top-tier GOP debate began on CNN at 8:30 p.m. EST from the Venetian Hotel in Las Vegas. Wolf Blitzer was tapped to moderate the forum, which focused on terrorism and national security. He was joined by panelists CNN anchor Dana Bash and conservative talk radio host Hugh Hewitt.

Four candidates -- former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum, South Carolina Sen. Lindsey Graham, and former New York Gov. George Pataki -- participated in the undercard debate, which aired before the prime-time forum.

The sixth Republican debate and first 2016 debate will be held Jan. 14 in South Carolina at the North Charleston Coliseum and Performing Arts Center.