Attorney General Loretta Lynch defended President Obama’s new executive actions on guns during a Senate hearing Wednesday, as a top Republican put her department "on notice" about infringing on constitutional rights. 

“This subcommittee will have no part in undermining the Constitution and the rights that it protects," Sen. Richard Shelby, R-Ala., top Republican on the Senate Appropriations panel that held the hearing, told Lynch.  

Lynch testified before the panel as the president's recently announced measures to expand background checks kick up an election-year fight over gun rights. GOP presidential candidates and lawmakers have condemned the president's move as an overreach of executive powers. 

Shelby almost immediately questioned the administration’s legal justification for moving ahead on its own and bypassing Congress.

“It is clear to me that the American people are fearful that President Obama is eager to strip them of their Second Amendment rights,” Shelby, who is up for re-election in November, said. “Let me be clear: the Second Amendment is not a suggestion. It is an individual right protected in the Bill of Rights that has been recognized by the Supreme Court.” 

But Lynch called the moves "well-reasoned measures, well within existing legal authorities, built on work that's already underway."

"I have complete confidence that the common-sense steps announced by the president are lawful," Lynch said. 

Obama's actions include new guidance on who the government will consider "in the business" of selling firearms -- a phrase used to describe which dealers must obtain federal licenses and conduct background checks on buyers. Even those selling a few guns online or at gun shows can be required to get licenses and perform background checks, the administration said.

Other steps include hiring 230 more FBI examiners so more background checks can be run; 200 additional agents for the Bureau of Alcohol, Tobacco, Firearms and Explosives; federal research on gun safety technology and a request for $500 million to improve mental health programs.

Lynch said Obama's 2017 budget, to be released in February, will seek $80 million for his gun proposals, largely for the additional FBI and ATF agents.

GOP presidential candidates Donald Trump and Jeb Bush have said they would repeal Obama's orders if elected, while Sen. Ted Cruz of Texas, another contender, called them unconstitutional. House Republicans said they will create a task force to study "executive overreach" by Obama and other presidents.

Most Democrats have supported Obama's actions.

"I'm fighting to give the Justice Department the tools they need to protect families and communities from gun violence," said Maryland Sen. Barbara Mikulski, top Democrat on the Appropriations panel.

Gun violence has grown anew as a political issue as mass shootings continue to rip through America. Obama failed to push gun curbs through Congress in the months following the 2012 killings of 20 children and six educators in Newtown, Connecticut, and the GOP-led House and Senate remain opposed to restricting firearms.

As Obama has conceded, Lynch told the senators she has "no illusions that these measures by themselves will end gun violence in America." She said she hoped Congress would work with the administration on the issue. 

Government statistics show that over 30,000 Americans die from firearms yearly, two-thirds of which are suicides.

The Associated Press contributed to this report.