Targeting keywords for multiple topics in 1 video

Broccoli Shmoccoli

Liking YTtalk
If you make a video about two of the most popular/trending/searched things at the same time and split the keywords between the two and target the keywords for both, will the video rank as good as a video that is specifically on one of the two topics and has keywords targeted just for one of the two things? I worry it won't rank well for any of the two topics... Do you know how to target for two topics at the time in 1 video?