If primaries say anything about general elections, then Cardin is more done than Burns.
But in reality, they do not. Burns has all the momentum and Montana is a red state. Tester peaked early and he's obviously out of answers.
The first part of this post, about having primaries doing nothing to do with anything, was great. Then you got to this ridiculous "momentum" crap. By and large, by the time we see momentum, it's over. There are some cases - the crash in TN - being an exception. But the movement has generally been within MoE range, which is simply not enough to establish that the numbers just didn't happen to fall that way.
I don't disagree that Burns has gained there, but I do dispute that you can call it a definite "trend."
EDIT: Just to clarify. I don't mean to say that there isn't momentum, but the problem with momentum is that it tends to end quickly and it's hard to tell when. I don't see it any more likely that his momentum will continue than won't, and if it doesn't, I think he'll still be behind. Which is a bad position to be in.
Momentum means less than pundits say it means. People won't start flocking to a candidate once his poll numbers go up. It's simple polisci.