Texas being competitive is a big deal -- and not necessarily for the reason you might think. Remember that when it comes to spending on the Senate majority, Newton's third law applies: Every action has an equal and opposite reaction. That's not a big deal when, say, North Dakota's Senate race becomes surprisingly competitive. Which means, in simple terms, a competitive Senate race in Texas is going to take tens of millions of dollars in spending for Republicans to move the needle for Cruz. CORRECTION: This story has been updated to correct the number of seats Democrats need to win back the Senate majority.

Source: CNN September 10, 2018 16:45 UTC