WASHINGTON — When the state of Alabama executed Ronald Bert Smith Jr. last week, he became the 20th inmate put to death in the United States this year. Smith’s execution was a rarity for the United States, where the death penalty is still retained in most states and on the federal level but, in practice, is carried out only in a shrinking handful of places.

No other lethal injections are scheduled for this month, meaning Smith will probably be the last inmate executed this year in the United States. As a result, the country is on track to end 2016 with its lowest number of executions in 25 years.

The decline in executions continues a recent trend, as 2016 will be the fourth consecutive year with fewer executions than the year before. It also speaks to a country that has shifted away from the death penalty in many places, while those states still trying to execute inmates have struggled with court challenges, drug shortages, and issues with carrying out the executions.

Overall, though, the trend is clear. Since a peak of 98 in 1999, executions have steadily declined, falling this year to the lowest total since 1991, when 14 inmates were put to death.

This year’s decline can be attributed, in part, to a handful of states that are among the most active practitioners of capital punishment but have been sidelined for part or all of 2016.

Florida has carried out the fourth most executions nationwide since the Supreme Court reinstated the death penalty in 1976. Its death penalty has been in flux for much of this year, ever since the Supreme Court struck down its system of imposing death sentences in January.

After this ruling, in Hurst v. Florida, lawmakers rewrote the death-penalty statute, but this new version was promptly struck down by the Florida Supreme Court. Nearly a year after the Hurst ruling, it is still unclear what will happen to Florida’s nearly 400 death row inmates.

In some cases, states hoping to carry out executions have been delayed by an inability to get the drugs needed for lethal injections, still the country’s primary method of capital punishment.

Ohio stopped executions for what will ultimately be at least three years while it sought new drugs.