Rubio, Paul spar over defense spending

What began as a disagreement over child tax credits between Sens. Rand Paul, Ky., and Marco Rubio, Fla., Tuesday evening quickly turned into a heated battle over what is necessary to ensure America's strength and security.

The nearly five-minute exchange during the fourth GOP debate began when Paul sharply criticized Rubio's call for an increase in the child tax credit, calling it a "welfare transfer payment."

"Yes, I have a child tax credit increase and I'm proud of it," Rubio told the crowd in Milwaukee minutes after he declared American families "the most important institution in the country."

"When we set out to do tax reform, we endeavored to have a pro-family tax code. And we endeavored to do it because we know how expensive it is for families in the 21st century to afford the cost of living," he added.

Paul, who described himself as the "only fiscal conservative on stage" during the third Republican debate, interjected with a question about fiscal conservatism.