The filibuster is expected to go through the night, against fast-tracked nominees by the Trump Administration. Booker’s protest appears to be in response to a recent wave of Republican nominees being fast-tracked through the confirmation process, many of whom are aligned with Trump’s second-term agenda and Elon Musk’s increasingly influential role in federal advisory circles.
It’s a solo filibuster, but Schumer has been asking questions to give Booker a break. This is the first time a filibuster has been applicable this term. Congress hasn’t been passing legislation. All of the damage has been done by executive order.
Edit: Murphy, Kim, and Gillibrand have also joined in with lengthy multi-part questions to support Booker.