Could a redirected asteroid big enough to damage the Earth evade detection long enough to do so?

A major plot point of a popular modern sci-fi series has a militant
faction redirecting asteroids to bombard Earth. Can we expect the
technology to detect and deflect inbound asteroids to advance on pace
with the technology to acquire and weaponize one?

Ooo, is it:

Spoiler

The Expanse?

Ding!

Phil Plait points out that we already have the technology to redirect asteroids:

But our current limitation is detection. “We need space telescopes out some distance from Earth that can sweep the volume of space toward the Sun that we can’t see from here.”