Wall Street's investment banks are advising clients on what to expect from the 2018 midterm elections and how to invest around those outcomes.

While most of the banks still expect the Democrats to take back the House of Representatives and split Congress, some analysts suggest chances are increasing for a Republican or Democratic sweep.

Bank of America Merrill Lynch, for example, told clients "we still think a split Congress is the most likely outcome but the probability of a 'blue wave' election in the House appears to have diminished."

Goldman Sachs suggested investors keep an eye on pharmaceutical stocks, which could rally if Congress ends up divided, the bank speculates. The firm's strategist contends a split Congress reduces the likelihood of an agreement to reduce drug prices.

Others highlighted the importance of trade policy and implications for U.S.-Chinese relations.

Here's what Wall Street is telling clients going into the 2018 midterm elections: