Air resistance applies a force opposite to the direction of travel (retrograde). At any given instant, the effect is to not change your direction of movement, but decrease your speed of movement. A retrograde force will always lower every point of your orbit (except the exact point where the force was applied, which would remain on your orbit). Since your orbit already has a point that intersects the surface of the planet, your new orbit must also intersect the surface.

One minor complication: Technically, air resistance applies a retrograde force relative to the direction of the wind. At low speeds this might actually increase your orbital velocity. However, the speeds where this is relevant are so small that they are not worth consideration.