St. Louis, Missouri (CNN) - Mitt Romney fired off on the Obama White House while speaking at the National Rifle Association Annual Meeting in St. Louis on Friday, tearing into the president for what he called the administration's attack on freedom.
"The right to bear arms is so plainly stated, so unambiguous, that liberals have a hard time challenging it directly. Instead, they've been employing every imaginable ploy to restrict it," he said.
His speech marks the launch of the general election campaign against the president, his advisers said Friday.
"This, is in our view, is the beginning of crystallizing for voters the choice that they are going to have in the fall between a big government liberal, represented by Barack Obama, and somebody who believes in the freedoms which are an essential part of our Constitution, which are consistent with our founders, and that would be Mitt Romney," said a senior adviser to Romney who briefed reporters before the speech but would only speak under the condition of anonymity.
The NRA speech is the first in a series of speeches that Romney will deliver in the coming months to "clearly define the choice in this race."
The adviser would not announce dates and topics for the future speeches.
Though Romney spoke before an audience of gun enthusiasts, a constituency he has awkwardly courted over the years, his remarks focused not just on Second Amendment rights.
Instead, he framed his remarks in the broader context of the Constitution and accused President Obama of attacking "economic freedom, religious freedom, and personal freedom."
"This President is moving us away from our Founders' vision," Romney said. "Instead of limited government, he is leading us toward limited freedom and limited opportunity."
Asked which specific gun rights the president has abridged since taking office, a Romney adviser would not say, but pointed to the Justice Department's handling of the "Fast and Furious" scandal and "the way in which that was used to provide cover for potential efforts to restrict Second Amendment rights."
The advisers were also asked to elaborate on two shotguns that Romney now owns.
The former Massachusetts governor announced in February that he owns the guns, but his campaign offered few details on when he acquired them or where they are kept.
"I am not going to disclose where those are kept for safety an security reasons," one Romney adviser said.