Former Virginia Gov. Terry McAuliffe told CNN on Saturday he's going "all in" to endorse former Vice President Joe Biden for president after thinking "long and hard" about who to support.

Why it matters: It's another boost for Biden and his campaign after he was projected to win the South Carolina Democratic primary and ahead of Super Tuesday. Virginia is a key state in those polls.

What he's saying: "For me, it's about beating Donald Trump and it's an electability issue," McAuliffe told CNN. "Joe Biden has the best chance of winning Virginia in the general election."

Go deeper: Joe Biden wins South Carolina primary

Editor's note: This article has been updated with comment from McAuliffe and more context.