The tweet you posted is wrong.
CBP has CBP Officers and Border Patrol Agents. Neither is an independent militia group. All are federal employees.
The guy isolated in the photo is union president Brandon Judd, who is a current Border Patrol Officer. He IS the guy who initially endorsed the Senate border bill. I already explained their position in other posts. NBPC generally opposes the Biden Administration border policy.
Judd attended the Trump event in his capacity as union leader, not an on-duty officer. It may interest you to know that CBP personnel were assigned to the Brownsville, TX event. Their presence was a job requirement, not an endorsement.
The National Border Patrol Council (NBPC) is a labor union established in 1967 representing approximately 18,000 Border Patrol agents and support staff on the United States Border Patrol.