I don't actually bother watching political debates since they are designed by the networks to showcase their on-air talent. Little useful can be drawn from watching them. I will read transcripts, but mostly I focus on the candidates actions the day after important debates.
Signs a Candidate Won
~ The candidate goes about his/her business, ignoring the previous nights events. This is a sign of confidence, it shows the candidate thinks he/she did well.
~ The candidate quotes her/himself on a policy point. Another positive sign. This shows the candidate fell in love with a pithy turn of phrase and thinks it hit the mark.
Signs a Candidate Lost
~ The candidate quotes him/herself attacking the opponent. This is always negative. It shows the candidate thinks the attacks didn't stick and that he/she has to pick up the mud and throw it again. (Simply put: Quoting self on policy, good. Quoting self attacking, bad)
~ The candidate (and surrogates) invests the entire newscycle correcting statements made in the debate. One or two corrections are okay, but if the entire day is consumed making corrections it is a sign the candidate figures she/he really screwed up.
~ The candidate disappears the next day. Planned events are canceled. The candidate goes into a shell for several hours or all day. This shows the candidate is either depressed or trying to reshape the whole campaign on the fly. It could also mean the candidate caught a cold. So watch out for the simpler health explanation.
Remember my axiom: It is far easier to lose a candidate debate than it is to win. The best outcome is a draw. This means that the more a candidate seems focused on the previous night's debate the worse he/she did. Winners move on; losers dwell on the past.