The fact is, when wolves attack a herd, they always take the weakest animal.
At the autumn equinox, the gate is weakest.
Zwingli attacked the weakest part of Luther's theory - the ubiquity of the body of Christ; and Luther attacked Zwingli's exegesis of the words of the institution.
The weakest pair of concave lenses with which one can read clearly test types at a distance of 18 ft.
Weakest, because he has no source of power.