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Thousands of people showed up to hear Republican presidential frontrunner Donald Trump speak at an Alabama rally Friday, in which the business tycoon vowed, "we’re going to make America better than it’s ever been."

The crowd filled about half of the 43,000-seat Ladd-Peebles Stadium in Mobile. It was a hot night, and humid. Trump looked upwards and joked: "If it rains, I’ll take off my hat and I'll prove, I'll prove, I'll prove once and for all, that it's mine," while stroking his hair.

Trump repeated his tough stance on immigration, vowing "we're going to build a wall," and saying Congress could end the guarantee of being granted citizenship upon being born within the U.S.

"The 14th Amendment — I was right on it. You can do something with it, and you can do something fast," Trump said. "In the case of other countries, including Mexcio, they don’t do that. It doesn’t work that way. ... We’re the only place just about that’s stupid enough to do it," he said.

Panorama of crowd and stadium here in Mobile. #trump. pic.twitter.com/rLDMDzIrKo — Katy Tur (@KatyTurNBC) August 22, 2015

Trump's campaign had pegged the expected attendance at the event at 42,000. They moved Friday's "pep rally" from the city’s Civic Center — which seats about 4,000 — to the stadium in anticipation of the huge crowd.

Police and fire officials estimated Friday's crowd at around 20,000.

Stadium is about half filled. Closer to 20,000 rather than the 40,000 campaign had hoped. Still largest Republican rally yet by far. #trump — Katy Tur (@KatyTurNBC) August 22, 2015

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Trump got some of his biggest cheers from the crowd Friday when he pledged to strengthen the military and take care of veterans, and when he extolled his skills as a businessman — while taking a swipe at GOP rival Jeb Bush.

"Who would you rather have negotiate with China, Japan, Mexico, any other: Trump or Bush?" Trump asked. The crowd cheered, and some began to chant "Trump! Trump! Trump!"

Trump has been drawing large crowds during stops in key primary states like New Hampshire, animating conservative voters who admire Trump’s brand of brash, often personal politics and his draconian proposals to upend the nation’s immigration policy.

"The more he speaks on issues — and he's an unfiltered candidate when he speaks — the more he does seem to resonate with folks," said Terry Lathan, the chairwoman of the Alabama Republican Party. "People like straight talkers and he seems to be doing that."

Last weekend, Trump unveiled an immigration blueprint that included the construction of a continuous border wall, the deportation of the nation’s estimated 11 million undocumented immigrants and the ending of birthright citizenship for children born on U.S. soil to parents in the country illegally.

Alabama, which will hold its presidential primary along with a slate of other southern states on March 1, 2016, could be particularly fertile ground for Trump’s message.

In spring 2011, the state enacted the nation’s harshest law to crack down on illegal immigration, including a provision requiring police to detain anyone suspected of being in the country illegally if the person was unable to produce proper documentation. The law also included a provision requiring public schools to determine the immigration status of students.

But a series of lawsuits swiftly resulted in the halting of many of the law’s key provisions, which opponents decried as blatantly unconstitutional. By October, the state reached a settlement agreement that effectively gutted the measure.

The state’s Hispanic population was about 4.1 percent in 2013, according to Census figures. But that number has been growing. Between 2000-2012, Alabama was one of the five states nationwide with the fastest growth of its Hispanic population, which grew 157 percent over the 12 year period.

Alabama is also heavily conservative, backing Mitt Romney by 61 percent over Barack Obama’s 38 percent in the 2012 presidential election.

Trump’s appearance in the state is intended to build support as the Republican field courts the southern voters who will weigh in on the primary contest shortly after key states like Iowa and New Hampshire.

But Gov. Robert Bentley, who signed the controversial 2011 immigration measure into law, is backing a different Republican for the 2016 race.

Earlier this week, Bentley backed fellow Republican Gov. John Kasich of Ohio, highlighting Kasich’s compassion and commitment to helping all Americans.

"We need someone who believes in the promise of our great country," Bentley said in his endorsement. "Someone who believes our country can be better and stronger and safer not only for those of us who maybe have a little bit more but those of us who in this country who need to be taken care of. ...It doesn't matter whether or not you're the same race, it doesn't matter if you're the same economic status. We need a leader who cares about the people."