The pressure on the Chinese economy is beginning to take its toll in other places, too. China’s currency, the renminbi, has fallen more than 9 percent against the dollar in the last six months and China’s CSI 300 index of blue chip stocks is off 19 percent this year.

Such concerning signals emanating from a country that accounts for roughly 15 percent of the world economy might give some investors pause. But for now, investors in the United States seem to see China as someone else’s problem.

The Standard & Poor’s 500-stock index is up more than six percent this year and continues to hover just below its record high, thanks to the health of the American economy. That growth — plus the windfall of deep tax cuts — has translated into gushers of corporate profits. Second-quarter earnings reports from companies in the S.&P. 500 are up roughly 25 percent from last year.

But if the slump in copper prices is a harbinger of a significant slowdown in global economic growth, American investors could eventually feel the pain.

Large American companies rely on sales outside of the United States for substantial portions of their revenue. Last year, 44 percent of the revenues of companies in the S.&P. 500 came from foreign countries, with Asia being the single largest regional source of sales, according to data from S.&P. Dow Jones Indices.

Investors seem broadly split over whether American markets can continue to separate themselves from worries about global growth.

In early August, Bank of America Merrill Lynch surveyed 185 money managers with over $500 billion in assets. One question asked whether the American economy could continue outperform the rest of the world.