"If Republicans continue to cower to the NRA," says Democratic presidential contender Kamala Harris, she will impose new gun controls by "executive action." If Congress does not change the law, in other words, Harris will, although that is not part of the president's constitutional job description.

The California senator's campaign website promises that "if Congress fails to send comprehensive gun safety legislation to Harris' desk within her first 100 days as president—including universal background checks, an assault weapons ban, and the repeal of the NRA's corporate gun manufacturer and dealer immunity bill—she will take executive action to keep our kids and communities safe." Harris does not claim that as president she could unilaterally ban "assault weapons" or repeal the Protection of Lawful Commerce in Arms Act. But she does claim she could change the law in two other significant ways.

Harris thinks the president can "mandate near-universal background checks by requiring anyone who sells five or more guns per year to run a background check on all gun sales." Since only federally licensed dealers are legally required to run background checks, such a rule would require dramatically expanding that category.

The problem is that federal law defines a gun dealer as someone who is "engaged in the business of selling firearms," which in turn is defined as a "devot[ing] time, attention, and labor to dealing in firearms as a regular course of trade or business with the principal objective of livelihood and profit through the repetitive purchase and resale of firearms." The statutory definition explicitly excludes "a person who makes occasional sales, exchanges, or purchases of firearms for the enhancement of a personal collection or for a hobby, or who sells all or part of his personal collection of firearms." Under Harris' plan, which she discussed on CNN yesterday, a hobbyist or collector who sold more than four guns in a single year would be required to obtain a federal license and conduct background checks, which is plainly inconsistent with current law.

Likewise Harris' plan to "close the 'boyfriend loophole' to prevent dating partners convicted of domestic violence from purchasing guns." Under current law, people convicted of misdemeanors involving "domestic violence" are barred from possessing firearms. But crimes against dating partners count as "domestic violence" only if the perpetrator has lived with the victim or produced a child with him or her. The House version of the bill reauthorizing the Violence Against Women Act would eliminate those requirements. Harris seems to think she can accomplish the same thing without new congressional action, but it's hard to see how. Congress has defined "misdemeanor crime of domestic violence," and only Congress can change the definition.

In trying to impose new gun restrictions by presidential fiat, Harris would be taking a page from Donald Trump, who demanded an administrative ban on "bump stocks" that required twisting the statutory definition of machine guns beyond recognition. Barack Obama also tried to expand gun control without congressional approval, although his administration did not go nearly as far as Harris proposes, and it recognized that banning bump stocks was inconsistent with existing law. It is telling that Harris believes voters who are appalled by Trump's power grabs would welcome a Democratic president who thinks she can ignore the law as long as they like her policies.