Growing up, I remember my parents telling me about the vice president’s role in the Senate. As president of the Senate, the VP only casts a vote in the event of a 50-50 tie among the senators. Thus, the VP rarely ever casts a vote.
But, as my parents explained, the VP’s vote only matters if there is a tie. If the Senate’s vote was 51-49, or 63-37, or 100-0, the VP’s vote will not change the outcome. So, functionally speaking, the VP has full voting power in the Senate.
For quick review, the Senate only votes on a bill if 60 senators vote to close debate. (If not, someone can “filibuster,” or aimlessly continue creating fake debate, to prevent an actual binding vote.) Thus, despite only needing 51 votes to pass a bill, you really need the tacit approval of 60 senators.
And there’s the rub. The VP does not vote on ending debate. Thus, he is powerless to stop the filibuster. In turn, for the VP’s tie-breaking authority to matter, it must be the case that at least 60 senators tacitly approve of a bill but exactly 50 of them are actually willing to sign off on it.
That’s a big caveat. Essentially, the filibuster nerfs the VP’s voting power.