Keep Particles When Reactivating Niagara

I am trying to switch from Cascade to Niagara. I am facing this issue:

In Cascade, I created a flame spell (similar to the one in Skyrim). I placed in on my character’s hand. Whenever I press the mouse button, the particle system (PS) is “Activated” and the particles spawn. When I release the mouse button, the PS is “Deactivated”, but the particles remain (desired). When I press the mouse button again, the PS is activated and the particles from the previous activation still remain (desired).

In Niagara, the particles from the previous activation do not remain when I activate the PS a second time. My Emitter inactive state is set to “Complete” but it doesn’t fix it. How do I keep the previous particles when I reactive the Niagara PS?