The Court described the two approaches as follows:
"Under some statutes, using a categorical approach requires the court to come up with a “generic” version of a
crime—that is, the elements of “the offense as commonly
understood.” We have required
that step when the statute refers generally to an offense
without specifying its elements. In that situation, the court
must define the offense so that it can compare elements, not
labels. For example, in Taylor, confronted with ACCA’s unadorned reference to 'burglary,' we identified the elements
of 'generic burglary' based on the 'sense in which the term
is now used in the criminal codes of most States."
"In contrast, other statutes calling for a categorical approach ask the court to determine not whether the prior
conviction was for a certain offense, but whether the conviction meets some other criterion. For example, in Kawashima v. Holder, 565 U. S. 478 (2012), we applied a categorical approach to a statute assigning immigration
consequences to prior convictions for “an offense that . . .
involves fraud or deceit” with a loss exceeding $10,000.
§1101(a)(43)(M)(i). The quoted language, we held, “mean[s]
offenses with elements that necessarily entail fraudulent or deceitful conduct.” Id., at 484 (emphasis added). Consequently, no identification of generic offense elements was
necessary; we simply asked whether the prior convictions
before us met that measure.
The Court was unanimous in holding that section 924(e)(2)(A)(ii)’s “serious drug offense” definition requires
only that the state offense involve the conduct specified in the statute;
it does not require that the state offense match certain generic offenses. In other words, the second of the two categorical methodologies applied.
I'm hopeful this will be less confusing in practice than it sounds. Basically, (I think) when the federal statute refers to what is well-established as a distinct criminal offense -- e.g., robbery, burglary, extortion -- but does not include the elements, the categorical approach will require defining the generic offense.
On the other hand, when the federal statute refers to conduct that is not itself a crime -- e.g., possession, distribution, deceit -- the categorical approach does not require identification of a generic crime. Instead, the question is whether that conduct was an element of the predicate conviction.
To be sure, this will not always be straightforward, but it is now the law of the land.
In other news, in Holguin-Hernandez v. United States, 589 U.S. ---, No. 18-7739 (2020), the Supreme Court held there is no need to object to the reasonableness of the sentence in order to preserve a claim on appeal that the sentence is too long.
This is because a defendant who, by advocating for a particular sentence, communicates to the
trial judge his view that a longer sentence is "greater than necessary" has thereby informed the court of the legal error at issue in an appellate challenge to the substantive reasonableness of the sentence. This was already the law in the 9th Cir.