The Russell 2000 Index has surged nearly 22% this year, posting its best first-half performance since 1991. "It's both a valuation catch-up story and a fundamental story," said Amy Zhang, portfolio ...

It is easy to think of artificial intelligence investing as a mega-cap story. After all, the AI boom has been led by some of the largest companies in the market, from chipmakers like Nvidia Corp.

Every bull market since 2016 has been a mega cap story. The S&P 500’s gains over the past decade have been driven by a handful of growth giants whose weight in the index keeps expanding. Three growth ...