Re: Mid Term US Election
US Senators serve a six-year term and elections are held every two years. Therefore, roughly one-third of the seats in the Senate are up for grabs every two years. Each state has two Senators for a total of 100. As far as I know, it's rare for the majority party to have a crazy number of seats more than the minority, so a big enough swing in the voting could theoretically lead to a different party winding up in control of the Senate every two years.
The House of Representatives is a little more complicated, but representatives only serve a two-year term and there's a total of 435 of them, so the political climate can change there pretty rapidly, though I'm honestly not sure that it does.
Other than these details, LonePhantom's post is essentially correct. Also, this thread does not appear to be a discussion of politics in any way and as such shouldn't run the risk of offending anyone or breaking any rules (in my opinion).