The report is that South Carolina Governor Nikki Haley will be endorsing Marco Rubio for President tonight. If true, it's a good get for Rubio: Governor Haley is popular in her state and a potential candidate for Vice President, and she's been keeping her endorsement back accordingly. And it's an endorsement that all the candidates wanted.
Not much else to say on this, really. If this pans out (it probably will, but better safe than sorry), then this is objectively a win for the Rubio campaign, but it's not a game-changer. It may be a sign that flow of the game is changing in Rubio's favor, but that's not the same thing. After all, the way we keep score here is by who gets the actual votes.
PS: Play close attention to everybody who reacts poorly to this news. Note, carefully, who they support. Calibrate your support accordingly.