“It’s not even about Scott Brown. It’s about: Do you want Elizabeth Warren in the Senate?”

Mr. Brown’s relationship with the financial industry owes in part to circumstance. He is one of few Republican senators in a region that is home to the nation’s most important financial centers, providing an open door and friendly ear to a executives who often lean Republican in their political giving but whose representatives in Washington are predominantly Democrats.

And his record on Wall Street issues is hardly one-sided: He provided the crucial 60th vote needed for the financial overhaul, known as Dodd-Frank, which Ms. Warren praised as “the strongest set of financial reforms in three generations” when it passed. And Mr. Brown angered banks in June when he voted against a measure that would have delayed a rule restricting billions of dollars in fees that banks charged merchants for debit card transactions.

But Ms. Warren’s advocacy for tighter financial regulation is so widely abhorred by Wall Street executives, some said, that lingering annoyance over Mr. Brown’s occasional heresies is rapidly evaporating.

“It’s not even about Scott Brown,” said one Wall Street executive, who asked for anonymity to discuss private discussions with his colleagues about the race. “It’s about: Do you want Elizabeth Warren in the Senate?”