Job growth has been consistent among counties that voted most strongly for Trump Average fourth-quarter-over-fourth-quarter growth, weighted by population · Source: Quarterly Census of Employment and Wages

In places like Montgomery County, Tex., and Pickens County, S.C., which voted for President Trump by more than 45 percentage points in 2016, the job market surged during the first two years of his administration.

Questions remain, though, about how much of the improvement was his doing, and whether the pattern is already in the process of reversing.

Data released Wednesday by the Bureau of Labor Statistics showed that average employment grew by 1.6 percent in 2018 in the 10 percent of places — 1,256 counties — that voted for Mr. Trump most strongly. Job growth did not rise as quickly in counties that supported him by a smaller margin and in counties that voted for Hillary Clinton.

Before President Trump took office, employment growth in the counties that favored him by more than 45 percentage points was nearly zero. But almost one year into his presidency, job growth picked up in these places.

Although President Trump has often credited himself for the job growth that has taken place in red states, the cause seems most related to deep shifts in the global economy that coincided with the start of his presidency.

Employment in counties won by Trump is now growing a little faster than in counties won by Clinton 12-month percent change in employment Source: Brookings analysis of the Quarterly Census of Employment and Wages

Earlier reports hinted that this rebound in pro-Trump counties might have been a temporary blip, but a second year of even stronger employment growth followed the first one.

“I think there’s a real sense that there may be some forward motion in these places,” said Mark Muro, a senior fellow at the Brookings Institution, who published a similar analysis.

Mr. Muro says there’s little evidence that the growth in these counties is a direct result of Trump administration policies. If anything, he argues, some of its policies might be a drag — like the trade war with China, which has resulted in retaliatory tariffs with a disproportionate effect on the counties that voted for Mr. Trump.

Instead, what appears to have happened is that these places recovered from a little-noticed mini-recession that rocked key industries disproportionately located in strongly pro-Trump counties.

Education and health services I.T., finance and professional services Agriculture, mining and manufacturing

In 2015 and 2016, oil prices dropped; demand from emerging markets dried up; and investment slowed. This hurt sectors like energy and manufacturing, but few outside these industries noticed because nationwide unemployment was still low and growth still positive.

The downturn took a toll on these deep-red counties. Their growth was nearly three-quarters of a percentage point less on average than for other counties.

But a few years of higher oil prices and improved global growth helped. The growth average in such counties moved slightly ahead of growth in the ones that voted for Mrs. Clinton.

This highlights a problem for these deeply Trump counties: their reliance on volatile industries. Sectors like manufacturing, energy and agriculture are more vulnerable to the vagaries of currency markets, global markets and economic policy, according to Jed Kolko, chief economist at Indeed and an occasional Upshot contributor. Blue places rely more on service-sector industries like health, technology and finance, which are more resistant to such fluctuations. They also still account for the majority of employment in America.

Mr. Kolko also cautions that this pattern of strong growth in Trump counties may not last much longer. He points to less fine-grained but more recent 2019 state-level employment figures from April showing that blue states are growing faster than red states.

Employment in goods and services Monthly year over year growth · Source: Bureau of Labor Statistics