The filibuster was launched by Democratic Senator Chris Murphy. Hes from Connecticut, where the 2012 mass shooting at Sandy Hook Elementary School occurred.
The filibuster was launched by Democratic Senator Chris Murphy. He's from Connecticut, where the 2012 mass shooting at Sandy Hook Elementary School occurred. CSPAN

Politico:

Sen. Chris Murphy (D-Conn.) launched a talking filibuster on the Senate floor — which was quickly joined by fellow Democrats — in an effort to pressure Republicans to accept legislation that would deny suspected terrorists from purchasing firearms and require universal background checks.

The Senate is debating a spending bill that Democrats hope to offer gun amendments to, but Murphy said that the Senate should “not proceed with debate on amendments to this bill until we have figured out a way to come together on, at the very least, two simple ideas.”

Watch here as some members of Congress actually try to do something.