Electromagnets cannot be made stronger

Answer 1

The 'strength' (flux density) of an electromagnet is limited by the saturation point of its core. Once saturation is reached, any further increase in current through the coil can have no effect on the flux density.

Answer 2

-- gluing heavy weights to it

-- painting it red

-- hanging it on the wall

-- shouting at it

-- soaking it in brine

-- making it do exercises

-- heating it

-- freezing it

-- taking it for a ride in the car

-- reading to it

-- whipping it

-- encouraging it