IN ALMOST every developed country, life expectancy at birth has trended predictably and steadily upward for decades, with slight hiccups from time to time, usually lasting just a year and often triggered by major epidemics. The United States, in the grip of an escalating opioid addiction and overdose crisis, has now recorded its second straight year of declining life expectancy, a nearly unheard-of event for a rich Western nation and its first such downturn in nearly 60 years.

That should be a wake-up call for the Trump administration, which has talked a fine game about the opioid epidemic but done too little to address it. A far greater sense of urgency is needed to address what has become one of the gravest public-health threats to the United States in living memory.

On Dec. 21, the Centers for Disease Control and Prevention reported that life expectancy in 2016 fell to 78.6 years, a second consecutive and statistically significant annual decline of a tenth of a year. The back-to-back drops coincided with an average annual increase in opioid-related overdose deaths of about 20 percent, and a staggering one-year surge in 2016 in which 42,249 people — an official tally that may understate the real scope of the problem by thousands — died of that cause. More bad news: Early signs are that drug-related deaths continued to climb in 2017, which could contribute to a third straight year of falling life expectancy, something that hasn't happened since the Spanish flu swept the country a century ago.

It would be a mistake to see the fall in life expectancy as part of a broad decline in American public health. Infant mortality continues to drop, and death rates from heart disease, cancer, flu, diabetes, kidney disease and other causes are mainly flat or falling. Rather, the main culprits are known as "diseases of despair" — especially drug overdoses and suicide. And the main victims are men, especially working-class young and middle-aged men, for whom the overdose death rate is twice that of women.

Mindful of the soaring toll, President Trump appointed a presidential commission on combating drug addiction and the opioid crisis, which recommended last summer that the president declare a national emergency, as he has pledged to do. That would have freed up funding from the national Disaster Relief Fund. Instead, in October he declared a public-health emergency, a lesser designation and one that has not unlocked game- ­changing amounts of federal dollars.

At the highest levels, the administration's response to the crisis has been sluggish, characterized by boastful rhetoric but stagnant funding. Mr. Trump has spoken of the government producing "really tough, really big, really great advertising," as if a Nancy Reagan just-say-no approach were adequate to the task of tackling a complex public-health scourge. He said the administration would crack down on the synthetic opioid fentanyl, manufactured in China, and endeavor to develop nonaddictive painkillers as an alternative to opioids. But where is the funding?