These are the key quotes in fourth Republican debate

Republican candidates covered plenty of political ground during their party's fourth primary debate of the 2016 presidential race, from immigration and the Islamic State group to taxes and Hillary Clinton.

Here are 10 of the best quotes by the eight candidates on stage in Milwaukee, Wisconsin:

BACK TO THE PAST

"First of all, thank you for not asking me what I said in the 10th grade."

-- Retired neurosurgeon and co-frontrunner Ben Carson, after a week of intense vetting by reporters who looked deep into his past, including his own personal accounts of his violent adolescence half a century ago.

BRICK BY BRICK

"If you think walls don't work, all you have to do is ask Israel."

-- Billionaire frontrunner Donald Trump, on his controversial plans to build a wall on the southern US border with Mexico.

THE CLINTON WAY

"A Clinton presidency will corrode the character of this nation. Why? Because of the Clinton way. Say whatever you have to, lie as long as you can get away with it."

-- Former Hewlett-Packard chief executive Carly Fiorina, offering sharp criticism of the likely Democratic nominee.

PILING ON HILLARY

"Hillary Clinton has said that Barack Obama's policies get an 'A' -- really?"

-- Former Florida governor Jeb Bush, who listed woes of the Obama administration, ranging from a discouraged work force to high poverty levels to kids on food stamps.

FLEXING US MUSCLE

"I know the world is a safer and better place when America is the strongest military power in the world."

-- Senator Marco Rubio, offering his argument for beefed up US national security operations and military expenditures.

DANGERS OF DEPORTATION

"We all know you can't pick them up and ship them back across the border. It is a silly argument. It is not an adult argument."

-- Ohio Governor John Kasich, attacking Trump's immigration plan as unrealistic.

TAXES AIN'T SCRIPTURE

"There are more words in the IRS code than there are in the Bible, and not a one of them is as good."

-- Senator Ted Cruz, criticizing Washington's current tax system and calling for a simple across-the-board flat tax of 10 percent.

SLASH AND BURN

"I want a government really, really small, so small you can barely see it."-- Senator Rand Paul, describing his call for balancing the budget and implementing a flat tax that shifts less money to Washington.

FIGHTING EXTREMISM, THROUGH RUSSIA

"If (Vladimir) Putin wants to knock the hell out of ISIS, I'm all for it 100 percent."

-- Trump, repeating his controversial position of supporting Russian intervention in Syria if it helps defeat Islamic State extremists.

GROUNDBREAKING TECHNOLOGY

"It took the telephone 75 years to reach 100 million users. It took 'Candy Crush' one year to reach 100 million users."

-- Rubio, explaining rapid changes in a 21st century world that are leading to an economic transformation.