Donald Trump has questioned whether rival candidate Ted Cruz is eligible to become a GOP nominee because he was born in Canada.

The Republican presidential front-runner called it a “very precarious” issue for the party and said that Ted Cruz’s nomination could be challenged in court.

Ted Cruz was born in Calgary to an American mother and a Cuban father.

Most legal experts believe Ted Cruz meets the requirements to be president.

The Cruz campaign responded by saying Donald Trump had “jumped the shark” – a pop culture reference to when a TV show or fad has overreached and fallen into decline.

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The Texas senator is performing well in polling in the early voting state of Iowa. While Donald Trump leads most polls, several surveys show Ted Cruz is the top choice of likely Republican voters.

Candidates for US president must be a “natural born citizen” – interpreted as being born in the US or having one parent who is a US citizen; be 35 years of age or older; live in the US for the past 14 years.

Much of Donald Trump’s support comes from independents, disillusioned Democrats and people who have never voted before.

Some analysts are predicting that Ted Cruz will win because of how the voting process is structured in Iowa.

The caucus format requires more time and dedication from voters than a typical US primary election.

Before Donald Trump became a presidential candidate, the New York tycoon had repeatedly questioned President Barack Obama’s citizenship.

Barack Obama was born in Hawaii to an American mother and a Kenyan father.

Authorities in Hawaii and Barack Obama both provided detailed birth records after some conservatives such as Donald Trump questioned where he was born.

Barack Obama’s allies have said the “birther” movement was a racist effort to discredit the county’s first black president.