Republican Presidential candidate Jeb Bush cast doubt on rival Donald Trump's judgment and ability to lead the United States in a complex world, saying the Republican front-runner discusses foreign policy like a reality show star.
In an interview with CNN that aired Sunday, former Florida Governor Bush added he has "grave doubts" about real estate mogul Trump's ability to appropriately handle America's nuclear weapons.
"He's not taking the responsibility, the possibility of being president of the United States really seriously," Bush said. "Across the spectrum of foreign policy, Trump talks about things as though he's still on The Apprentice."
'Not a serious approach'
Bush told CNN that Trump's proposed plan of hoping the Islamic State group removes Syrian President Bashar Assad from power and then Russia taking on the Islamist extremists is like "some kind of board game and not a serious approach."
"This is just another example of the lack of seriousness. And this is a serious time. We're under grave threats again, and I think we need a president with a steady hand," Bush said.
Trump fired back immediately on Twitter, saying "Jeb, why did your brother (former President George W. Bush) attack and destabilize the Middle East by attacking Iraq when there were no weapons of mass destruction? Bad info?"
The latest CBS News poll shows 27 percent of Republican primary voters support Trump, giving him a six-point lead over his closest competitor, neurosurgeon Ben Carson, with 21 percent.
The rest of the Republican field is in single digits, including Bush with just 7 percent.
In a separate CNN interview, Democratic presidential front-runner Hillary Clinton said it was too soon to say whether she would bring all U.S. troops home from Afghanistan if elected to the White House.
President Barack Obama last week halted the withdrawal of U.S. military forces from Afghanistan, announcing that the United States will keep thousands of troops in the country through the end of his term in 2017.
Clinton praised Obama as a commander-in-chief with "strong convictions of what he would like to see happen" – bringing U.S. forces home – tempered by "what he sees going on in the real world."
Mitt Romney, the Republican's presidential nominee in 2012, slammed Clinton's tenure as secretary of state, saying American interests abroad deteriorated during her time in office.
He also defended a House committee's controversial investigation into the 2012 Benghazi attack.