As he departs the White House, President Trump speaks about the partial government shutdown, now in its fourth week. (Jim Lo Scalzo/EPA-EFE)

In recent days, the White House and several Republican lawmakers have floated the idea of using asset forfeiture money held by the Justice Department to cover the initial cost of Donald Trump’s proposed border wall. The proposal has drawn harsh criticism from civil libertarians, including some in the president’s own party.

Below is a primer on this highly contentious law enforcement practice that’s drawn fire from critics on the left, right and center in recent years.

What is asset forfeiture?

Asset forfeiture is a legal mechanism that allows authorities to seize and, provided certain conditions are met, permanently keep cash and property from people suspected of crimes. Forfeiture can happen under the criminal justice system, which requires a criminal conviction in order for property to be permanently forfeited. But it can also proceed under civil law, which does not require a conviction or even a criminal charge to be filed.

Why is asset forfeiture controversial?

Because civil forfeiture does not require a criminal charge to be filed, cash and property can be taken from individuals who are never convicted of any wrongdoing. A Washington Post investigation documented that between 2001 and 2014, police seized at least $2.5 billion from people who were not charged with a crime. And a 2017 report by the DOJ’s inspector general found that since 2007 the Drug Enforcement Administration took at least $3.2 billion in cash from people not charged with a crime.

Stories abound of authorities seizing large amounts of cash from individuals who were eventually cleared of any wrongdoing: A convenience store owner in North Carolina. A 64-year-old immigrant living in Ohio. A college student. The tour manager of a Burmese Christian rock band.

When a law enforcement agency forfeits property, it typically gets to keep it for itself, to be used for things such as buying new equipment and paying for staff bonuses. Critics of the practice allege that the ease of forfeiting property and the broad discretion agencies have to use it creates a profit motive. Research from the Institute for Justice, a civil liberties law firm that represents forfeiture defendants, has found that forfeitures increased in eras of budget cuts.

How much forfeiture money does the federal government have?

In fiscal year 2018, the DOJ’s asset forfeiture fund had a net balance of about $1.5 billion, roughly triple the balance that was in there in 2001. The Treasury Department maintains a separate asset forfeiture fund with a balance of $2.2 billion as of fiscal year 2017 (more recent data from the Treasury is not yet available).

While the federal government does not release detailed breakdowns on the source of those funds, previous research by the Institute for Justice found that 87 percent of federal forfeiture proceedings advanced on a civil basis, rather than a criminal one. That means that large amounts of that money were taken from individuals never convicted of any crime. Taking money seized from these individuals and putting it toward an unpopular presidential policy priority would probably be highly controversial.

Can the federal forfeiture money be put toward the wall?

Under federal law, money from the DOJ’s forfeiture fund can only be put toward certain specified uses, including maintaining the fund itself, paying overtime and salaries of law enforcement officers, paying informants and upgrading law enforcement vehicles. Similar rules govern the money in the Treasury Department’s forfeiture fund. Absent congressional action, authorities wishing to appropriate money for a wall from either fund would have to justify that use under existing statutes, and it’s unclear whether they’d be able to. ABC News’s Tara Palmieri has reported that Justice Department officials are “fiercely against” using DOJ forfeiture money in this fashion.

Could the forfeiture fund pay for the entire wall?

No. A 2017 internal report by the Department of Homeland Security estimated the cost of the wall to be $21.6 billion. That’s more than 10 times the total amount in the Justice Department’s forfeiture fund as of 2018. Even adding the entirety of the funds in the Treasury forfeiture account as of 2017 would only account for a fraction of the total cost.

The latest known balances of both funds, in fact, only add up to $3.7 billion — $2 billion less than President Trump’s $5.7 billion funding demand to reopen the federal government. Even in the highly unlikely scenario in which both forfeiture funds were zeroed out completely, there would still be billions in additional funding required to completely build the wall.