Stock Pullback Has Investors Debating How Deep Selloff Will Go

The biggest slump in a month for US stocks is leading investors to question whether long-running concerns over lofty tech valuations, narrow market breadth and economic uncertainty will finally bring an end to the bull run that started in April.

Risk assets slid around the world Tuesday, fanned by a chorus of Wall Street executives who warned about a pullback. The S&P 500 Index fell 1.2%, its biggest decline since Oct. 10, while a gauge of tech megacaps lost 2.3%. Shares favored by retail investors tumbled the most since the chaos in April caused by Donald Trump’s trade war. Stocks ...