Everybody. They might vote for you, they might contribute money (in return for favors after the election), they might have intelligence (dirt) you can use, they might put in a good word for you, they might be planning a stab in the back. You never know, so you talk to everybody you have time for. You want to increase your candidate's name recognition, talking about him with everybody will increase it.
Given all that, I fail to see any interest in today's msm flap about Trump campaign workers, (Donald Trump Jr and Jared Kushner) talking with a low name recognition Russian lawyer. So what? Everybody in the world wants something from the US, everybody in the world starts by talking to the presidential campaign people. So what else is new?