the crucial experiment; cast the deciding vote; the determinative (or determinant) battle.
the deciding vote cast by the presiding officer to resolve a tie.
In close cases, the court typically divides along ideological lines, with Mr Kennedy casting the deciding vote.
The Supreme Court is polarised, too-so much so that it might strike down Obamacare, the President's flagship achievement, on the deciding vote of a single judge.
The Chairman shall preside at all meetings of the Board of Directors and shall cast the deciding vote in the case of a tie.