Dr. Ben Carson reportedly attracted 12,000 people to a rally in Phoenix, Arizona, on Tuesday night, topping the crowd Donald Trump and Bernie Sanders attracted to the same space in recent weeks.

Speaking on the eve of the candidate’s planned tour of the southern border, Carson tackled immigration, touching on unsubstantiated claims that terrorists will cross American borders and announced his support for eliminating birthright citizenship, saying “it doesn’t make any sense to me.”

The speech – a rambling address filled with attacks on the media and a litany of Republican talking points – was received by cheering crowds. Though the event was originally scheduled for a smaller venue, it was moved to the Phoenix Convention Center to accommodate the nearly 10,000 people who RSVPed to attend.

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The politically inexperienced doctor – who famously compared Obamacare to slavery – seemed an unlikely candidate for the highest office when he announced his campaign in May, but his best-selling books and rags-to-riches stories have resonated on the campaign trail. Tuesday’s rally – in addition to the large crowd he drew at the Iowa State Fair – signals that Carson has secured a significant place within the 2016 Republican primary field.

Echoing the kind of immigration rhetoric that has amplified Trump’s candidacy, Carson advocated “sealing” the country’s four borders.

“A lot of people think it’s just because of people coming from south of the border, but there are radical, global jihadists who want to destroy us and our way of life and we have to keep them out,” he said, hinting at a familiar claim that the Islamic State and other terrorist groups are flooding the American borders illegally. This claim has not been substantiated.

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“Illegal immigration will stop when America “turn[s] off the spigot that dispenses the goodies, there cannot be any goodies for people,” Carson said. “It won’t be worth trying to get through our borders if there are no goodies – and that includes employment. We should make it illegal to employ people who are not here illegally, it’s as simple as that.”

It is already illegal to knowingly employ an undocumented immigrant.

Carson is polling well: In the CNN/ORC poll released on Tuesday, he ranked third, with 9% of registered Republican voters supporting him.

“All the pundits say it’s impossible and they say you can’t put together an organization and you can’t raise money,” Carson said. “However, I just said, ‘Lord, if you want me to do it, you open the doors and, if you open the doors, I will walk through.’”