This morning Trump said in his address to the nation that the ballistic missiles fired from Iran did minimal damage and that there were no casualties.
Looking at these maps from CNN of the aftermath of the bombings does indeed show that the missiles they fired were not that effective:
According to Fox News the Al Assad has a perimeter of more than 15 miles, so it’s a very large base about 100 miles west of Baghdad.
Just based on what I see in these maps, it really doesn’t look like these were precision hits at all. It would make sense that there were no casualties even if the US had only learned about the attack as the missiles were in the air. Clearly Iran didn’t really want war with the US, and they chose correctly.