WASHINGTON (NewsNation) — President Joe Biden on Monday nominated Obama-era U.S. attorney Steve Dettlebach to run the Bureau of Alcohol, Tobacco, Firearms and Explosives, as his administration moves to formally rein in ghost guns, privately made firearms that usually are assembled from parts from gun kits and lack the serial numbers used to trace them.

Dettlebach served as a U.S. attorney in Ohio from 2009 to 2016, and his nomination is likely to be an uphill battle for the Biden administration. Biden had to withdraw the nomination of his first ATF nominee, gun-control advocate David Chipman, after the nomination stalled for months because of opposition from Republicans and some Democrats in the Senate.

The administration also released the finalized version of its ghost gun rule, which comes as the White House and the Justice Department have been under growing pressure to crack down on gun deaths and violent crime in the U.S., sources told the Associated Press.

So-called ghost gun kits are self-assembled from parts purchased online or at gun shows and are increasingly associated with crimes. But they are not classified as firearms and so can be legally sold without serial numbers or background checks.

“These guns are weapons of choice for many criminals,” Biden said Monday. “We’re going to do everything we can to deprive them of that choice and when we find them, put them in jail for a long, long time.”

For years, federal officials have brought attention to an increasing black market for homemade, military-style semi-automatic rifles and handguns. Ghost guns have increasingly turned up at crime scenes and in recent years have been turning up more and more when federal agents are purchasing guns in undercover operations from gang members and other criminals.

Justice Department statistics show that nearly 24,000 ghost guns were recovered by law enforcement at crime scenes and reported to the government from 2016 to 2020. It is hard to say how many are circulating on the streets, in part because in many cases police departments don’t contact the government about the guns because they can’t be traced.

Biden previously attempted to tighten regulations of buyers of self-assembled untraceable “ghost guns” last year in a bid to tackle gun violence in the United States. For nearly a year, the ghost gun rule has been making its way through the federal regulation process. Gun safety groups and Democrats in Congress have been pushing for the Justice Department to finish the rule for months. It will probably be met with heavy resistance from gun groups and draw litigation in the coming weeks.

The rule is expected to change the current definition of a firearm under federal law to include unfinished parts, like the frame of a handgun or the receiver of a long gun.

Some states, like California, have enacted laws in recent years requiring serial numbers to be stamped on ghost guns. The ATF has said more than 30% of the illegal weapons it has confiscated in some areas of California are ghost guns.

The critical component in building an untraceable gun is what is known as the lower receiver, a part typically made of metal or polymer. An unfinished receiver — sometimes referred to as an “80-percent receiver” — can be legally bought online with no serial numbers or other markings on it, no license required.

Police across the country have been reporting spikes in ghost guns being recovered by officers. The New York Police Department, for example, said officers found 131 unserialized firearms since January.

Requiring serial numbers even for what have been considered unfinished firearms, would aid law enforcement, Biden said.

“All of the sudden it’s no longer a ghost. It has a return address,” he said.

A gunman who killed his wife and four others in Northern California in 2017 who had been prohibited from owning firearms built his own to skirt the court order before his rampage. And in 2019, a teenager used a homemade handgun to fatally shoot two classmates and wound three others at a school in Southern California.