Donald Trump bashed Republican presidential rival Ted Cruz for stealing his immigration reform plan.

According to The Hill, Trump claimed credit for being the first GOP candidate to come up with the idea of building a wall to better secure the U.S.-Mexico border.

"I was watching the other day, and I was watching Ted talk, and he said, 'We will build a wall,'" Trump said. "The first time I've ever heard him say it."

At that point, Trump said his wife pointed out the Texas senator was "copying what you've been saying for a long period of time."

Trump later added he is not concerned about recent polls showing Cruz now leading him in the critical, early voting state of Iowa.

"You know, nobody says it, in Iowa, the CNN poll, it's 33 to 20 that I'm leading," he said. "Ted Cruz is second. Nobody ever talks about that poll. I have a real good feeling with Iowa."

With the race between the two GOP front-runners seemingly tightening, in recent days Trump has taken to even questioning Cruz's legal eligibility for assuming the Oval Office.

"Republicans are going to have to ask themselves the question: 'Do we want a candidate who could be tied up in court for two years?'" Trump said in reference to Cruz's Canadian birth. "That'd be a big problem."

The Constitution requires presidents to be "natural-born citizens." The children of American citizens who are born abroad are automatically granted citizenship. Cruz was born in Canada, but his mother was an American citizen.

The bombastic Trump has long made an issue of President Obama's citizenship and Hawaiian birthplace, even after the president released his long-form birth certificate in 2011.

Another of Trump's more controversial stances during his campaign has been his boast that, if elected, he would deport some 11 million immigrants in less than two years.