THE MORNING PLUM:

Today, President Obama will roll out his new executive actions on guns, and the action that is most likely to generate a lot of noisy controversy and criticism is the one designed to expand federal background checks to gun sales that were previously not covered by them.

Yet, based on what we know now, it actually may prove to be a fairly modest change — both legally and in substantive terms. Here is how it works.

Here is what the new initiative does: It clarifies which gun-sellers are supposed to obtain a federal firearms license. Since guns sold by licensed dealers are subject to federal background checks, and guns sold by private sellers are not, this change, by extension, would also clarify which additional gun sales are subject to background checks. Gun reformers believe that some private sellers are selling guns regularly in a manner that allows more gun sales to elude background checks and to slip into the hands of prohibited buyers. This clarification would attempt to prevent that.

Here is the policy challenge: The difficulty is how to go about clarifying which additional private gun sellers should obtain licenses and conduct background checks on sales. Current law says that those who are “engaged in the business” of selling firearms, “with the principle objective of livelihood and profit,” are required to get a license, and thus to run checks. But the law excludes those who make “occasional” sales or sell their personal firearms collections.

President Obama formally announced a set of executive orders on gun control on Jan.5. Here is what you need to know about how the regulations tighten gun sales and expand background checks. (Claritza Jimenez/The Washington Post)

Thus, the challenge here is to redefine “engaged in the business” in a manner that captures those who effectively are engaged in the business of selling guns — but currently are operating without a license — without capturing those who aren’t. This turns out to be harder to do than expected.

Here is how the new change meets that challenge: According to multiple reports, and to experts I spoke with who have been briefed, the change does not set a threshold number of gun sales that, once crossed, would suddenly require a seller to get a license. This is because setting a threshold number could actually be counterproductive. If the threshold is high — say, 100 guns a year — a seller who peddles a few dozen per year regularly would not be required to get a license. But if the threshold is low — say, five guns in a year — that could wrongly require someone selling a lot of guns from a private collection to get a license.

“If you set the threshold low, it could open this up to legal challenges,” Arkadi Gerney, a gun law expert at the Center for American Progress, tells me. Indeed, as I reported recently, the administration looked at this approach and found it unworkable and legally vulnerable.

Instead, the new executive action articulates a variety of other indicators that determine a seller to be “engaged in the business” of selling firearms, and thus to require a federal license. Gerney, who was briefed on the changes, tells me they will include items such as: Whether the seller prints business cards; whether the seller accepts credit cards; and whether the seller uses a regular venue, such as a rented table at gun shows. Other indicators may include whether the seller has a website advertising sales.

“Using multiple indicia is more consistent with the statute and will make this tighter and smarter,” Gerney says. We still need to see the details to be certain of how this will work, but those are the basic outlines.

Is this a big change? Not really, according to Jonathan Adler, a law professor at Case Western Reserve University who was a leading architect of the King v. Burwell legal challenge to Obamacare subsidies. Adler says the overall impact will probably be to require a license for those who should have gotten one anyway. “It looks like it’s just a guidance that brings clarity,” Adler says. “That is, it doesn’t really capture anyone who should not have already been complying with relevant requirements.” Adler’s conclusion: “this particular step is modest.”

One imagines the GOP presidential candidates, who have already denounced Obama’s executive actions as an assault on the Second Amendment, will not be easily persuaded of this initiative’s modesty.

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Update: The new guidelines are now online right here.

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* OBAMA PLANS OTHER EXECUTIVE ACTIONS: Here are some of the other ones:

Obama would devote $500 million more in federal funds to treating mental illness — a move that could require congressional approval — and require that firearms lost in transit between a manufacturer and a seller be reported to federal authorities. At the president’s direction, the FBI will begin hiring more than 230 additional examiners and other personnel to help process new background checks 24 hours a day, seven days a week.

Also, the Bureau of Alcohol, Tobacco, Firearms and Explosives has established a new investigation center to keep track of illegal gun trafficking online and will devote $4 million and additional personnel to enhance the National Integrated Ballistics Information Network.

Gerney tells me that taken all together, these actions could have a “substantial” impact. It’s unclear how much of an impact the most controversial of these — the background check initiative — will have.

 * OBAMA’S GUN ACTIONS COULD BE HELD UP BY COURTS: The Post aso reports that the administration expects the new executive actions to be targeted by a legal challenge, and adds:

One dilemma for the Obama administration would be that a legal fight could put the executive actions on hold as a court deliberates, potentially dragging out the process until Obama leaves office next January. The president’s executive actions to defer the deportations of millions of undocumented immigrants, announced in 2014, have been held up in a legal battle that could head to the Supreme Court this spring.

As I’ve noted, it could actually be a good thing if this goes to the courts, because it’s possible the Supreme Court could end up affirming the constitutionality of background checks.

* TRUMP CONTINUES TO DOMINATE: A new NBC/Survey Monkey poll finds that Donald Trump continues to hold a large lead among Republicans and GOP-leaning independents nationally: He has 35 percent; Ted Cruz has 18 percent; and Marco Rubio has 13 percent.

Also note: Trump is dominating among white evangelicals, with 33 percent, and Cruz is second among them, at around 20 percent. White evangelicals are very important in many of the early contests.

* HILLARY HOLDS LARGE LEAD OVER SANDERS: The new NBC/Survey Monkey poll also finds that Hillary Clinton leads Bernie Sanders among Democrats and Dem-leaning independents nationally by 53-36. Key details: Sanders leads Clinton by 65-30 among “very liberal” Democrats, which helps explain why he may well win New Hampshire (and perhaps Iowa).

But Clinton leads by 73-12 among black voters, again suggesting she will likely hold a big edge in the later contests with more diverse electorates.

* GOP IN FULL-BLOWN PANIC ABOUT TRUMP, CRUZ: Politico reports that the panic is escalating among Republicans about the immense damage a Trump or Cruz nomination could do to the party and its hold on the Senate. Here’s how one senior GOP operative puts it:

“At some point, we have to deal with the fact that there are at least two candidates who could utterly destroy the Republican bench for a generation if they became the nominee. We’d be hard-pressed to elect a Republican dogcatcher north of the Mason-Dixon or west of the Mississippi.”

And yet, according to the polling averages, more than half of GOP primary voters support either of those two men. How inconvenient!

 * CONSERVATIVES PUT GOP CANDIDATES ON NOTICE: A major conservative group, Heritage Action for America, is set to send a letter to all the GOP candidates demanding a full and unconditional commitment to repealing Obamacare:

The group said the next Republican administration should agree to use all executive authority at its disposal to halt regulation of the insurance market under the new health law, ensure the new vice president presides over the Senate to guarantee “complete and full” repeal is achieved under special filibuster-proof rules, and then agree to sign a full repeal into law.

It will be interesting to see how conservatives respond if and when the eventual GOP nominee tries to argue that he has an alternative to Obamacare that might also spend federal money to cover people.

* GUN SALES SOARED AFTER SAN BERNADINO SHOOTING: The New York Times runs the numbers:

More guns were sold in December than almost any other month in nearly two decades, continuing a pattern of spikes in sales after terrorist attacks and calls for stricter gun-buying laws…The heaviest sales last month…followed a call from President Obama to make it harder to buy assault weapons after the terrorist attack in San Bernardino, Califoria.

In December, 1.6 million guns were sold. Don’t you feel safer already?