Flight Instructor with student reported a partial loss of engine power during cruise. Flight returned to departure airport.

Narrative

My day started normal beginning with adequate rest; breakfast; and an uneventful drive to the airport. My student was on time and ready. Debriefing and preflight occurred as normal; 5qt oil; no contaminants in fuel. Taxi and runup occurred as normal; less than 100rpm drop per mag with less than 50rpm between L and R. Taxi to Runway XX was uneventful along with takeoff and short climb to 2000' after clearing airspace. Student began clearing turns before I took controls. During a medium bank turn I experienced a power reduction; I attempted to remedy this by increasing power but this magnified the power loss. Immediately I reduced power to the previous setting to maintain altitude and decrease engine roughness.I switched back to ZZZ Tower frequency; established comms; and advised them of the engine trouble and my intention to return for landing. The Tower Controller gave me priority and full assistance and I continued east to the airport. I then ran the power loss in flight checklist. AS I minimized altitude lost; I entered ZZZ1 airspace without clearance; en route to ZZZ while flying a flight path that gave me suitable forced landing locations. Landing was uneventful and engine power remained adequate to taxi back to the FBO ramp.In hindsight I should have [requested priority handling] on initial contact with ZZZ. This would've allowed ATC to accurately see my position and maintain aircraft separation across all pertinent airspace.