Sforno on Deuteronomy 32:35/ספורנו על דברים ל״ב:ל״ה

1לי נקם, it is up to Me to do the avenging from My enemies.

2ושלם, also the repayment tit for tat is My privilege and duty.

3לעת תמוט רגלם, the time when this will occur will be when they are already perceived as tottering.