From Ars Technica:

A majority of senators—59 out of 100—supported the amendment. But under the Senate’s dysfunctional rules, it takes a 60-vote supermajority to end debate on a proposal like this and move to a vote. So even though a majority of senators supported the amendment, it did not become part of the reauthorization bill.
Four senators—Lamar Alexander (R-Tenn.), Patty Murray (D-Wash.), Bernie Sanders (I-Vt.), and Ben Sasse (R-Neb.) missed the vote. The amendment would have passed if any of them had voted “yes.”