Clinton’s ambitious plans, announced Monday, would mostly either require unlikely Republican help or raise questions about executive action in court

Hillary Clinton’s ambitious proposals to reduce gun violence – announced on Monday - have been applauded by reform advocates in the aftermath of the Oregon school shooting last week that left 10 dead, but most of her plans would either require unlikely Republican help or raise questions about executive action in court.

The fly in the ointment for Clinton’s plan – as it was for Barack Obama’s in the wake of the 2012 Sandy Hook school shooting – is Congress.

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Background checks

Clinton’s plan calls for closing the loopholes in background checks for people who want to buy guns. Currently, those buying guns privately online or at gun shows are allowed to do so without being subject to such checks.

The law also allows dealers to sell guns without a completed background check if that check takes longer than 72 hours to finish. Dylann Roof, the man who killed nine people in a church in Charleston, South Carolina, in July was thus able to buy a gun despite having a criminal record that should have barred him from making the purchase.

Clinton has proposed closing both the 72-hour and private-seller loophole, but unless she can rally Congress more forcefully than Obama has been able to her proposal will remain just that. In 2013 the Senate rejected a similar, Obama-backed measure, even though Americans overwhelmingly wanted to expand background checks at the time. Since then the Senate has fallen into the hands of Republicans staunchly opposed to any gun legislation.

If she were stymied by Congress, Clinton would use executive action to reclassify any person “attempting to sell a significant number of guns”, according to her campaign. People formerly considered “private sellers” – and thus exempt to the background check rule – would be recategorized as being “in the business” and would therefore be held to the same standards as licensed dealers, according to her plan.

This might have more success, suggested Adam Winkler, a UCLA law professor and specialist in gun control policy.

“Second amendment lawyers are very active in America today, and they’ll challenge anything they can,” Winkler told the Guardian, referring to the constitutional right to bear arms. “Any piece of legislation or executive action is almost certain to be challenged. But is it likely to be invalidated? I don’t think so.”

He added: “The laws on the books are ambiguous about how to define someone in the business of selling guns, and it’s the job of the president and the executive branch to interpret those laws.”

Conservatives have challenged Obama’s executive actions on immigration in court – so far without a clear result – but the president’s slew of executive actions meant to reduce gun violence, and his quiet push to expand background checks, have met less resistance. Clinton’s proposal is more ambitious, and would probably face a more concerted legal battle, depending on its details.

While Clinton would have trouble expanding background checks for gun shows without the agreement of Congress, Winkler said, she might have more success in holding online sellers to the standards of licensed dealers.

“When Congress passed the gun legislation there was no such thing as online sales,” he said, “so it’s not clear that they designed the law in a way that would impact them.”

More broadly, background checks may prove only moderately effective at reducing gun violence: some mass murderers, including the gunmen in Sandy Hook and Oregon, acquired their weapons legally. In May, Oregon expanded background checks to most gun sales.

Legal protections for gun manufacturers

The Democratic frontrunner also says she would urge Congress to repeal a law signed by George W Bush – and vigorously supported by the NRA – that granted gun manufacturers broad protections from liability for “the harm caused by those who criminally or unlawfully misuse firearm products”.

The law guards manufacturers and dealers against lawsuits from victims’ families, some of whom want to sue gunmakers to force them to include safety measures, such as biometric locks, in a similar tactic used to force auto makers to install seatbelts and airbags.

Courts have largely upheld Congress’s logic that people cannot sue gunmakers for the actions of a third party, meaning Clinton would again need to convince lawmakers to change their minds – and would then probably face continued legal challenges from manufacturers and lobby groups such as the NRA.

The former secretary of state would probably not have numbers on her side if she were to win the White House. Although Republicans have to defend 22 seats in the Senate, which they currently control, with about half in competitive states, Democrats face several key races with more disadvantages, including primary challengers and unpopular incumbents, than they might like, and the odds are also stacked against their chances of winning the 32 seats needed to reclaim the House.

Illegal gun sales

Clinton would also be able to direct the Justice Department to crack down on illegal gun sales, although prosecuting such crimes is difficult, Winkler said. “Going after someone who may have filled out a form improperly, and maybe putting them in jail for years – that’s a hard case to take to a jury,” he said.

“One of the ironies of our current system is that though you want to increase the penalties for people who make illegal sales, the more you increase the penalties the less likely people are to convict.”

Mental illness and domestic abusers

Clinton’s other plans that would require help from Congress include keeping guns out of the hands of people “suffering severe mental illness” and all domestic abusers, and cracking down on dealers who knowingly supply so-called straw purchasers – illegal sales in which someone buys a gun to deliver it to a third party – all proposals favored by gun reform groups.

Many in those groups expressed relief that presidential candidates were actually talking about gun control at all, in contrast to previous elections.

“This shows how significant a shift it is that this year, in this cycle, presidential hopefuls are proactively addressing the country’s gun violence problem,” said Erika Soto Lamb, communications director for Everytown for Gun Safety, which also released a set of gun control proposals on Monday.

Soto Lamb said Clinton’s proposals were a sign that voters “now expect for some of the people who want to be our leader to tell us how they’re going to fix this problem”.

Dan Gross, president of the Brady Campaign, another pro-gun control group, was more outspoken in his praise, saying in a statement: “This is exactly the type of leadership that has been sorely missing in Washington.”

Former congresswoman Gabrielle Giffords, a victim of a 2011 shooting and co-founder of Americans for Responsible Solutions, also applauded Clinton.

“While governing by executive action is no one’s first choice in making policy,” Giffords and her husband said in a statement, “the American people support closing the loopholes in our background check laws. In the face of Congress’s absolute refusal to do anything meaningful to reduce dangerous people’s access to guns, we think all options should be on the table.”