No one should underestimate his ideological role in Al Qaeda or his operational command.
In other words, underestimate the power of Roger Ailes only at your peril.
“I love it when they underestimate her,” Mansour told Draper.
1812, "to estimate at too low an amount," from under + estimate (v.). Meaning "to rank too low, undervalue" is recorded from 1850. Related: Underestimated; underestimating.