Hello KJV1611,
Just FYI, the "He" in the verse cannot be confirming and existing covenant and that because the decree was for seventy seven year periods. Sixty-nine of those were fulfilled when the Messiah was cut off. Now there remains one seven year period, which is what that ruler, the antichrist, is going to establish. He's the one who initiates that last seven years by making his covenant with Israel. To suggest that he is confirming an existing covenant would infer that it is longer the seven years.
The word "gabar" simply means "strong, mighty." It says nothing about confirming an already existing covenant. He is the one who will be making the covenant. Here is how the NLT translates it:
"The ruler will make a treaty with the people for a period of one set of seven, but after half this time, he will put an end to the sacrifices and offerings. And as a climax to all his terrible deeds, he will set up a sacrilegious object that causes desecration, until the fate decreed for this defiler is finally poured out on him."
Many of the translations have it as "he will make."