Something not to find in bed when you wake up

I'm not sure if this puzzle is themed. The clues seemed unrelated, especially that the first answer was in the format of a themed answer:

Assault - kindofrifle
Citation - courtsummons
Affirmed - corroborated
Rare event in horseracing - triplecrown

So I got all these, but the closest theme I can find was phrases with a hard K sound, which is a really stupid theme. So I checked out the NYT crosswords forum, and found that there was indeed a theme, but it wasn't in my area of expertise. Assault, Citation and Affirmed were all horses that have won the Triple Crown. How am I supposed to know this? Well, for future information, here are all 11 horses that have ever won the Triple Crown. Apparently, a coveted title in horseracing.

Affirmed - 1978
Seattle Slew - 1977
Secretariat - 1973
Citation - 1948
Assault - 1946
Count Fleet - 1943
Whirlaway - 1941
War Admiral - 1937
Omaha - 1935
Gallant Fox - 1930
Sir Barton - 1919