On Tuesday, Americans will go to the polls to choose their representatives in Congress, in the mid-term elections that are considered a referendum on President Donald Trump's policies and determine the balance of power within Congress during the last two years of his term. What is the most important thing we know about this election?

On Tuesday, Americans will go to the polls to choose their representatives in Congress, in the mid-term elections that are considered a referendum on President Donald Trump's policies and determine the balance of power within Congress during the last two years of his term. What is the most important thing we know about this election?