DES MOINES, Iowa –  Conservative heavyweights joined with up-and-comers in hammering the Obama administration Saturday over its record on national security, immigration and more as they played to a sold-out Iowa crowd in what amounted to the opening bell of the Republican presidential campaign.

Nobody on stage at the Iowa Freedom Summit in Des Moines has definitively declared a 2016 bid — but nearly a dozen speakers attending are flirting with one.

Testing their message on the conservative Iowa crowd, they took a hard line in their prescriptions for the country.

“The liberal policy agenda does not work and never will,” said Ben Carson, a neurosurgeon who has reinvented himself as an outspoken conservative and won an enthusiastic following in the process.

Drawing some of the biggest applause of the day, Carson took on the thorny subject of immigration, saying fixing the country’s immigration issues should rest on Congress’ shoulders and not the president’s – in a dig at President Obama’s executive actions.

Carson, who has been flirting with the idea of a 2016 presidential run, told the crowd the next president should “make it their goal to seal the border within a year.”

He said part of the problem is that the United States is too attractive to illegal immigrants. 

“We have to reverse the magnet,” he said. “We should not be employing illegal immigrants. Do we have the ability to seal the border? Yes. We don’t have the will.”

Carson suggested adopting a guest-worker program similar to the one Canada has and said anyone applying for guest-worker employment should do so while in another country.  

Carson also took on the Affordable Care Act and said “even if it worked, I would oppose it.”

Carson warned the crowd that health care should not be put in the hands of the government and said ObamaCare fundamentally changes America.

Donald Trump, too, told a revved-up audience he’d build an impenetrable wall to keep illegal immigrants out. “I’m Trump. I build things,” he said, while saying he’s “seriously thinking” of running for president.

The daylong event in the first-in-the-nation caucus state, which includes a packed schedule of speeches back-to-back, serves as the unofficial kickoff to the 2016 Republican presidential race. Among those on the guest list are New Jersey Gov. Chris Christie, Wisconsin Gov. Scott Walker, Texas Sen. Ted Cruz and former Texas Gov. Rick Perry, most set to speak later in the day.

Freshman Iowa Republican Sen. Joni Ernst, who gave the GOP response to the State of the Union address, also had tough words for the president’s record on fighting terrorism. Former Virginia Gov. Jim Gilmore told the crowd he was “ashamed” of that record and said the president should have gone to Paris to join the unity rally after the attacks in that city this month.

The summit is sponsored by Iowa GOP Rep. Steve King and Citizens United.

King, in his opening remarks, called for abolishing the IRS and going after Obama’s “executive overreach,” while largely sidestepping the broader immigration issue.

King, known for controversial statements on immigration, recently called a 21-year-old illegal immigrant who was Michelle Obama’s guest at the State of the Union address “a deportable.” He told an Iowa radio station Friday he was being “kind and gentle” with that description.

The incident became quick fodder for Democrats eager to cast Republicans attending as “extreme” on immigration. Democratic National Committee Chairwoman Debbie Wasserman Schultz, in a press conference across the street from the summit in Des Moines, called it an “extremist ring-kissing summit masquerading as a political forum.”

King, though, did not fuel the immigration fire in his opening remarks. Instead, he focused on the future and said the next president of the United States must “restore that separation of powers.”

He also took a jab at those in his party who declined to attend. (2012 GOP presidential nominee Mitt Romney, former Florida Gov. Jeb Bush and Kentucky Sen. Rand Paul are among those not in attendance.)

“Do you believe that the next president of the United States is going to be speaking from this stage to you today?” he asked. “As do I.” He was met with applause.

King said he wants Americans to elect a new president who is ready to sign legislation that will “rip ObamaCare out by the roots.” He also told the crowd he has penned a 40-word bill to make ObamaCare “as if it had never been enacted.” King pushed for a president who will restore respect for the U.S. Constitution “and in doing so, our next president can unleash the greatness of America.”