Donald Trump now has a commanding 14-point lead over Texas Senator Ted Cruz in their largely back-and-forth battle for the 2016 Republican presidential nomination.

According to CNN, a new Fox News national poll now shows Trump leading Cruz 34 percent to 20 percent, with Florida Senator Marco Rubio a distant third at 11 percent.

No other candidate from the crowded GOP field raches double-digit support, with retired neurosurgeon Ben Carson at 8 percent and former Florida Governor and former party front-runner Jeb Bush at just 4 percent.

Cruz Impacted by Citizenship Controversy

The poll also found that Cruz is being impacted by the growing issue of his citizenship. Researchers found that 10 percent of Republican primary voters now admit they are less likely to vote for him as the controversy stemming from his Canadian birth continues to swirl around his head.

Trump Goes on Attack

Recently, Trump made it an even bigger issue for some GOP voters by warning them the election of Cruz could allow Democrats to legally contend he isn't even allowed to hold the office of the president.

Overall, more than one-fourth of all voters surveyed in the poll, or 27 percent, responded Cruz is not eligible to be president. Among voters identifying as Democrat, those numbers swell to 38 percent, compared to 20 percent of Republicans.

The poll comes less than two weeks before the first votes are to be cast in the critical, early voting state of Iowa, where most polls find Cruz and Trump running neck and neck.

With the stakes so high, a growing number of Republicans are warning that the party would suffer deep losses down the ticket if Cruz were nominated, while the National Review, a leading conservative voice for decades, recently blistered Trump in editorial urging GOP voters to steer clear of him.

The poll, which ended on Jan. 18, was conducted by telephone over a three day period with live interviewers.