It's hard to know since you offer few details, but usually this is friction.

Could be with in the FD itself -- test by shifting by pushing down on the arm .to see if it moves easily or not

Or, friction where the wire passes below the bottom bracket, (or down from top tube on top pull), test by shifting by pulling the bare wire away from the down tube like a bow string (compare the the RD wire using the same method)

Or if not there, it could be in the handlebar/frame housing.

Also, know that often levers get harder to shift, both front and rear, when the cable is beginning to fray in the lever before breaking. If you can't identify a source of friction, you might need a new cable (replace housing at the same time).