The vote tally in the State Senate now stands at 31 of 62 members, with one more vote needed to approve the law. The Assembly has passed the measure several times before and is likely to do so again this week if the Senate moves ahead.

"I think I'm doing the right thing, it's the appropriate thing, and if the public respects that, I'm grateful," Mr. McDonald said as reporters pressed him in the Capitol for his decision. "If they don't, then I move on."