Important concept here: the federal bank, being the central bank, has to act independently from the US government. It enacts Monetary policy (in America's case, this refers to the manipulation of interest rates), while the government enacts fiscal policies (which refers to governmental spending, taxation etc). Both these policies work to expand/contract the economy in line with predetermined targets. 

With that said, the midterm election, in theory, should NOT have an impact on the feds decision of whether to raise, stagnate or drop interest rates. However, in practice, this might not be the case. Many policies that the government put in place can influence inflation, which is one of the indicator for the feds to set their target interest rates. A increase in budget spendings, for example, especially in the form of welfare handouts, would theoratically raise consumer spending, thus resulting in increased demand for goods and thus inflation, while austerity cuts would work in the reverse. 

The safest thing for traders to do would thus be to beware of the increased volitility during this time. Investors, on the other hand, can take advantage is this volitility, and should be on the lookout for stocks which are transiently going for lower than their market value, and have the capital in place to deploy the moment these stocks reaches their ideal prices.