Presumptive Republican presidential nominee Mitt Romney on Sunday said he wasn’t sure if he had ever paid an effective tax rate lower than 13.9 percent, and insisted that he wouldn’t even be qualified to be president if he paid “more than are legally due.”

During an interview in Israel, ABC’s David Muir noted that the candidate had only released two years worth of tax returns and had paid an effective rate of 13.9 percent in one of those years. Some have speculated that Romney may be refusing to release additional tax returns because he paid a substantially lower rate or virtually no taxes at all in previous years.

“Can we clear this up by asking a simple yes or no question?” Muir asked Romney. “Was there ever any year when you paid lower than 13.9 percent?”