Is there any legitimate reason for 45's campaign to have been talking to Russian Intellegence.

Lots of discussion around 'Did he or didn't he?', how often, and about what WRT Flynn, and maybe a few other 45 staffers. But I haven't come across anybody wondering why the staff of any campaign would be talking to Russian Intelligence to begin with. And that seems like a really obvious question to me. How would such communication be needed? Do presidential campaigns often converse with the Intelligence people of adversarial countries? (Or even friendly ones?) About what? Why? It looks like it was treason in this case, but when it happens in a 'normal' way, what's going on?

What do I not know about this?

(And my apologies if I've missed a previous discussion or am overlooking something obvious.)