To virtually eliminate the threat of a filibuster in the modern U.S. Senate, one party would need at least 60 senators.

Why 60 is the key number

  • Under current Senate rules, it usually takes three-fifths of all senators duly chosen and sworn to invoke cloture, which is the procedure to end debate and overcome a filibuster. In a 100-member Senate, that is 60 votes.
  • If a single party controls 60 or more seats , it can, in almost all routine situations, end debate on its own and move to a final vote, meaning the minority cannot sustain a filibuster.

A bit of context

  • Passing a bill after debate ends still only requires a simple majority (51 votes) , but the real choke point is getting to that vote by invoking cloture.
  • Because of this, people often say that the Senate today effectively operates as if most major legislation needs 60 votes to pass. One party having 60 members all but neutralizes the filibuster as a blocking tool on ordinary legislation.

So, the minimum number of senators from one party to virtually eliminate the threat of a filibuster is 60.

TL;DR: 60 senators from one party.