A quarter of Republicans think White House hopeful Ted Cruz is disqualified to serve as U.S. president because he was born in Canada to an American mother, a new Reuters/Ipsos poll found.

Republican voters nearly mirror independents and the broader electorate in their belief that Cruz cannot hold the White House, with 27 percent of all voters and 28 percent of independents responding he should be disqualified.

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Cruz, a U.S. Senator from Texas who was born to a U.S. citizen mother and Cuban father in Calgary, Alberta, has brushed aside the attacks about his eligibility as pure politics. But the questions could hamper his ability to rally the broad Republican support he would need to win the party’s nomination to run for the presidency in November’s election.

Only 47 percent of all voters surveyed responded that they thought Cruz is qualified to be president with regard to his citizenship, with 26 percent saying they were not sure.

The poll was taken from Jan. 7 to Jan. 14, before questions about Cruz’s eligibility became one of the most heated moments of Thursday night’s Republican primary debate.

New York businessman and reality TV star Donald Trump has made questions about Cruz’s eligibility a regular attack line on the campaign trail and the debate stage.

“I already know the Democrats are going to be bringing a suit. You have a big lawsuit over your head while you’re running, and if you become the nominee, who the hell knows if you can even serve in office?” Trump said during Thursday night’s debate. “So you should go out, get a declaratory judgment, let the courts decide.”

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But Cruz tried to use Trump’s own previous words against him in response.

“Back in September, my friend Donald said that he had his lawyers look at this from every which way and there was nothing to do this,” Cruz said. “Since September, the Constitution hasn’t changed, but the poll numbers have.”

Trump became a conservative darling in 2011 when he repeatedly questioned President Barack Obama’s eligibility to be president, insisting that the president may have been born in another country and demanding to see his birth certificate.

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Obama was born in Hawaii. It made Trump one of the most well-known “birthers,” a term used to describe those who insisted Obama had been born elsewhere.

The constitutional issue at question is the requirement that a president be a “natural born” citizen.

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Cruz, 45, has argued that because he became a citizen at the time he was born, that makes him qualify as natural born. But his opponents argue that at the time of the writing of the Constitution, natural born would have required being born on American soil.

U.S. Senator John McCain, who ran as the Republican nominee in 2008, was born in Panama, but argued he met the requirement because his birth took place on a U.S. military installation, which is the same as American soil.

The poll, which has a confidence interval of 5 percentage points, posed two questions to two separate polls of voters. One group was asked about Cruz’s eligibility. The other half was asked a generic question about the eligibility of anyone born in Canada with an American parent.

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(Reporting by Ginger Gibson and Chris Kahn; editing by Grant McCool)