、。
At last, the Communist found himself a powerful ally.
Literal
Finally, that communist [topic-は] strong-handed ally [obj-を] obtained.
ついに again marks culmination. 手づよい (手強い) is the compound adjective 手 'hand / skill' + 強い 'strong,' meaning 'tough / strong / formidable.' 味方 'ally / supporter' contrasts with 敵 'enemy.' 得る (える) is the formal verb 'to obtain / acquire,' more literary than 手に入れる. The whole sentence has the flavor of historical or political narrative.