The market veteran says trading volume should have picked up on Tuesday when the S&P 500 approached last week's highs.
"We punched through it marginally," said Cashin, UBS' director of floor operations at the NYSE. "We got right close to 2,050 but there was no follow-through. There was no explosion. There was no pickup."
That raises questions about the "decisiveness" of these record highs, Cashin said.