Secret Service Guns And Gear at the Trump Assassination Attempt
Remington 700 long actions in Accuracy International AX chassis systems. This video from 2016 shows the Remington markings on the receivers. The caliber is unknown, but these are likely chambered in .300 Win Mag or a ballistically similar cartridge like .300 Norma or .300 PRC.
USSS has a history with the .300 Win Mag cartridge, and in the video mentioned earlier, the fired brass appears to be belted, which is a good indicator that these rifles were chambered in .300 Win Mag as of 2016. That is not a guarantee that the same caliber is in use as of 2024, but it is a strong possibility. This rifle has a lot in common with the USMC Mk13 Mod7, though those rifles have FDE chassis and use a one-piece scope mount instead of the scope rings seen on the USSS guns.
http://www.thefirearmblog.com/blog/secret-service-guns-and-gear-of-july-13th-2024-44814994
Liberals are like a "Slinky". Totally useless, but somehow ya can't help but smile when you see one tumble down a flight of stairs!