As I see the text, it states:
--"confirm [/strengthen] a covenant" (likely ['strengthening'] one having already been in existence, "strengthening" it, i.e. putting it into effect)
--"with the many" (I can't say whether this "WITH" means "ALONG WITH" [as though all participants are doing same, ALONG WITH when THE OTHER IS ALSO] OR that this "WITH" means, "[with] TWO distinct PARTIES" [as in, he is one side, the many are the opposing side, but coming together FOR this "covenant"... such as a peace treaty would be, between two opposing parties coming together FOR that purpose);
--"[with] THE MANY" - it seems that Scripture elsewhere uses the phrase "the many" to refer to Israel (those in the nation of Israel), so where it says "WITH THE MANY," I don't want to say I know with certainty that it's "ALONG WITH the many" WHEN THEY DO [this thing, TOO]" (all together), OR as TWO opposing parties COMING TOGETHER FOR it (to "strengthen / confirm" it "FOR ONE WEEK [7 yrs]");
I do believe that "the prince THAT SHALL COME" (v.26b) is not saying he will exist when "the PEOPLE OF" him do the "shall destroy the city and the sanctuary" stuff in the first century (Lk21:23,20; Lk19:41-44; Matt22:7; etc); I DO believe "the prince THAT SHALL COME" is not [Jesus] / the Messiah the Prince of v.25,26a... but is DISTINCT from that reference (and corresponds with both 1Jn2:18 "YE HAVE HEARD [<--phrase pointing back to OT words] that antichrist IS COMING" and the "whose COMING" 2Th2:9a / Dan11:36-37 [PRIOR to MID-point in 12:1,6-7])
I could present much more... and will if you think more evidence is needed than what I've provided...
[to be clear, SEAL #1 rider on white horse [INITIAL "BP"] with the "BOW [/DECEPTION]"... who [will-future] "went forth conquering and to conquer" (at the START of the "IN QUICKNESS" time-period) IS the KICK-OFF of the "7 yr period... "Our Rapture" will have ALREADY taken place by that point (Rev5:9 "hast redeemed US... out-of EVERY...")]
Let me just add: I don't think 1Th5:3's "WHEN... SAY" means this lasts 3.5 yrs