Because two Democrat senators are currently hospitalized and not attending the current Senate session, including California's Dianne Feinstein, and another has left to attend to a death in the family, the party's slim majority has evaporated, and the Senate stands at 48-48 until one of the three returns.
Feinstein announced on Thursday that she was in the hospital with shingles and expected to return to the Senate later in the month.
Additionally, Sen. John Fetterman (D-PA) remains hospitalized for treatment of clinical depression, and Sen. Jeff Merkley (D-OR) had to go home to Oregon after his mother died earlier in the week.
Republicans would technically have the majority if it weren't for the fact that Sen. Mike Crapo (R-ID) is also absent after contracting the coronavirus.
With all of these absences, Vice President Kamala Harris has had to cast several tie-breaking votes.
Two of Biden's judicial nominees had to be confirmed with a vote from Harris, and more of those votes could be required before a true Democrat majority can be restored.