Well, you asked if the FTC did anything and they definitely did something. What credit they can claim for the eventual outcome is a different discussion but the answer to 'did they do anything' appears to be 'yes'.
Sorry, I should have made clear I meant "do anything to block the merger." That's what my reference to a preliminary injunction was about, but I realize this is a tech forum and not a law forum so I should have clarified.
The FTC's action certainly deters behavior. You don't need an actual court order and armed marshalls.