Former Florida Gov. Jeb Bush came out firing at rival presidential candidate Donald Trump at Saturday night's debate when asked about national security and Russian president Vladimir Putin. In particular, Bush maintained that Russian military forces were targeting Syrian rebels. Trump took an opposite stance, vehemently asserting that it has not been proven the rebels were acting in the best interest of the U.S.

When Bush was asked by the debate moderators about the war against the Islamic State group, also known as ISIS, in Syria, the former governor voiced his support for a coalition effort to defeat the terror organization.

bush Republican U.S. presidential candidates (L-R) former Florida Gov. Jeb Bush, Texas Sen. Ted Cruz, businessman Donald Trump and Florida Sen. Marco Rubio stand together Saturday night before the start of the Republican U.S. presidential debate sponsored by CBS News and the Republican National Committee in Greenville, South Carolina. Photo: REUTERS/Jonathan Ernst

"They're attacking the troops we're supporting," Bush said about the pro-Putin forces on the ground in Syria. "We need to destroy ISIS -- you can't do that with Assad in power."

In response, Trump fired back: "We’re supporting troops that we have no idea who they are.”

Later in the debate, the exchange took a more personal turn when Bush said he took umbrage to how Trump was routinely invoking his family's name, such as the billionaire's penchant for blaming the Sept. 11 terror attacks on former president George W. Bush. 

Bush was mad his family has been brought into the discussion, as Trump blamed former President George Bush for launching the war in Iraq under apparently disillusioned pretenses. When Trump said he lost hundreds of friends when the World Trade Center buildings fell, was consequently booed by the audience, one of multiple instances of those in attendance voicing their displeasure at the real estate mogul's comments Saturday night.

Bush entered Saturday night's debate up against his protégé, Florida Sen. Marco Rubio, as the two were in effect battling it out for third place. The former Florida governor, whose campaign has not been as successful as some political experts anticipated when his candidacy was announced last year, has resorted to having his mother, former first lady Barbara Bush, and his brother, former President George W. Bush, to come out on the campaign trail in order to ramp up support for his White House bid.

Businessman and rival candidate Donald Trump chastised that move, the latest barb tossed between the two as their war of words has heated up significantly in recent weeks. "I see he's bringing his brother in now. He tried the mother, who's a very nice lady, I'm sure, but he tried the mother. That didn't work out so good," Trump said Thursday, reported the Hill. "Now he's bringing in his brother."

In turn, Bush has expressed doubt at Trump's recent proclamation that his campaign would now be based more on "optimism" than his previously divisve rhetoric.