The stock market's post-election bifurcation sharpened Monday as technology shares extended their worst performance since the start of the bull market on speculation Donald Trump's trade and immigration policies will translate into lower earnings.

Apple Inc., Facebook Inc. and Alphabet Inc. led the S&P 500 Information Technology Index down 1.7 percent for the biggest retreat since September. The group stands out as the only industry that normally benefits from a rising economy not to rally on speculation Trump's policies will stoke domestic growth. Tech stocks in the benchmark equity gauge have slumped 3.1 percent over four days, trailing the S&P 500 Index by 4.2 percentage points, the most since May 2009. Small caps in the Russell 2000 Index surged 1.2 percent to an all-time high.

No single fact explains the tech rout though everything from trade and immigration policy to industry rotation to flat-out campaign retaliation have been cited. Technology is the biggest group in the S&P 500 by far and one of the only ones to consistently post earnings growth over the last 18 months.