They can test deflection methods on other asteroids, build large spacecraft launchers and have them ready to go, do surveys to make sure the N-body predictions

They can test deflection methods on other asteroids, build large spacecraft launchers and have them ready to go, do surveys to make sure the N-body predictions are as accurate as possible, etc. Some of that's being done (NEOWISE, DART) but if you want to deflect a planet killer you need a lot more.