If you are trying to figure out what might happen in the upcoming elections, I suggest you watch the stock market more than the polls. If the stock market is strong in my opinion the Republicans maintain one or both houses, especially the house of reps. The reason I say especially the house of reps is that this is generally the more radical of the two bodies and would be the likely place for any "investigations" or "impeachmnent talk".
The stock market does not like change. If you see the market beginning to drop sharply before the election, look for a big win by the Democrats. What's interesting is that these drops are often followed by rises shortly after the election is over but I wouldn't count on it yet. It depends on how vitriolic the Dems are if they gain control.