|Win? Lose? Draw?|
The U.S. House is controlled by the Republicans; the Senate is controlled by the Democrats. There are two independent Senators. Both of them "caucus"--that is, meet to do Senate business like form committees or decide strategy--with the Democrats.
The stakes are high this year. For example, in the mid-term election of 2010, the Republicans, helped by the tea party movement, won decisive control of the House.
In the presidential year, 2012, the Democrats gained two Senate seats. The House stayed in Republican control in part because their gains in 2010 were enough to withstand a higher national popular vote for Democrats. Republicans lost only 8 seats.
In 2013, the Republicans used their power to refuse approval of any government spending unless programs they didn't like were killed. Government spending by law has to be approved by Congress. The U.S. government was forced to "shut down" for almost 2 weeks in 2013. Only critical operations could take place. This crisis was resolved in a fairly short time only because Democrats controlled the US Senate. The House had to negotiate and a compromise was found.
How many U.S. Representatives a state has depends on its population. The state is divided into voting districts of approximately the same number of people. The lines that define the district can be manipulated. The states decide where the lines will go. This is one reason why it's important which party controls the state.
Since Republicans still control a majority of states, it is unlikely that there will be any major change in control of the U.S. House.
If the Democrats lose control of the Senate, it is probable that President Obama's policies and priorities will be extinguished.
That's the national overview. What exactly does Maine have to win (or lose) in the mid-term election?