Yes they did, on March 8th, and they did not mention if they warned the Russian authorities.
NooseWeak: Rare US Warning of Imminent 'Extremist' Attack Sparks Backlash in Russia
How did they know?? About an attack on March 21.
Because they were in on the planning, just like January 6th.
“Because they were in on the planning,”
Hey Johnny Walker Red, where’s your proof?