Republican presidential candidates are attacking President Obama’s plan to use his Oval Office powers to try to tighten gun-control laws, arguing his efforts are “unconstitutional” and another attempt to sidestep Congress.

"We're not changing the Second Amendment," front-running Donald Trump said Saturday at a campaign rally in Biloxi, Miss. "I will veto that. I will un-sign that so fast."

Obama said over the weekend that he’ll meet Monday with Attorney General Loretta Lynch to discuss his options on tightening federal firearms laws to reduce gun violence, after instructing his White House team several months ago to look at what type of “action” he could take.

“The president is a petulant child,” GOP candidate New Jersey Gov. Chris Christie told “Fox News Sunday.” “Whenever he doesn’t get what he wants, … this president acts like a king.”

Obama purportedly will use executive action to require small-scale gun sellers to order background checks on prospective buyers and tighten laws for gun sales to those who have committed domestic-abuse offenses.

“The president has a pattern of taking away rights of citizens,” GOP candidate and former Florida Gov. Jeb Bush told “Fox News Sunday.”

Bush also suggested that he didn’t object in principle to keeping guns out of the hands of criminals, but that he is wary of how far-reaching and burdensome the proposed changes might be on small-scale gun sellers.

“How do you know?” he asked. “The better approach would be to punish people who violate federal gun laws. … If it’s such a great idea, let (Obama) go to Congress.”

The president tried unsuccessfully in the aftermath of the 2012 mass shooting at Sandy Hook elementary school, in Newtown, Conn., to get Congress to pass comprehensive gun control legislation.

The National Rifle Association, which opposed that plan, also opposes the new plan, calling it a “political stunt.”

Christie and others point out that Obama has tried to use executive action to allow illegal immigrants to remain in the United States and work. However, a federal appeals court has temporarily stopped that action, pending a final ruling.

“I’m sure (the gun executive action) will get stopped by the courts,” Christie also said Sunday.

Trump, a billionaire businessman, on Sunday told CBS’s “Face the Nation” that if elected he would use the same executive powers to repeal Obama’s likely new executive orders on gun control.

“The one thing good about executive orders: The new president, if he comes in -- boom, first day, first hour, first minute, you can rescind that,” he said.

GOP candidate Carly Fiorina told CNN’s “State of the Union” that Obama “has been a lawless president” in his use of executive orders.

“It is delusional, dangerous, not to mention unconstitutional,” she said. “We have long lists of criminals who own guns, who routinely purchase guns. We know who these people are, and we are not prosecuting any of them.”

The three Democratic presidential candidates -- Hillary Clinton, former Maryland Gov. Martin O’Malley and Vermont Sen. Bernie Sanders -- support tighter gun control.

Sander told ABC's “This Week” he wishes Obama could get bipartisan congressional support but that he supports the president’s renewed efforts.

“There is a wide consensus. (The) overwhelming majority of the American people believe we should expand and strengthen the instant background checks,” he said. “I think that's what the president is trying to do, and I think that will be the right thing to do.”

Sanders also said he supports more background check, which would likely help close what gun-control advocates call the “gun show loophole" as well as strong measures to keep criminals and people with mental health issues from owning firearms.