WASHINGTON, Jan. 15 (Xinhua) -- The tension between Ted Cruz and Donald Trump, leading Republican contenders in the White House race, was on full display Thursday night at the latest debate that centered on Cruz's eligibility question.

　　Trump has attacked Cruz over his birth in Canada, saying it raised questions about his presidential eligibility.

　　At the debate in the State of South Carolina, Cruz accused Trump of focusing on his birth in Canada because of his strong poll numbers, saying "the Constitution hasn't changed, but the poll numbers changed."

　　Cruz also noted some "birther theories" say a candidate must have two parents born on U.S. soil to be eligible to run.

　　Pointing out Trump's mother was born in Scotland, Cruz said: "On the issue of citizenship, I'm not going to use your mother's birth against you."

　　Trump replied that Cruz wasn't doing so because it wouldn't work.

　　A new Wall Street Journal/NBC News poll finds that Trump has opened a double-digit lead over Cruz, less than three weeks before the first votes of the 2016 presidential race are cast.

　　The other contenders were trying to focus their attention on attacking president Barack Obama.

　　"On Tuesday night, I watched story time with Barack Obama, and it sounded like everything in the world was going amazing," said Chris Christie, governor of New Jersey.

　　Senator Marco Rubio said Obama had played down the threat of the Islamic State.