When it comes to the Senate, the correlation between results and presidential approval isn't nearly as high. That's because only one-third of senators are up for re-election every two years and, in this arena, it's the Democrats who have exposure.
"Six Democratics seats are in real danger and only four GOP seats are in danger," Cook said. The four Republican seats are in Arizona, Tennesee, Nevada and Texas.
Texas Senator Ted Cruz and former New York Mayor Michael Bloomberg are the two smartest people in American politics, in Cook's view, but Cruz is "charm-challenged." Texas may be getting less Republican but "a potted plant should win [as a Republican] in Texas."
It is possible that Democratic and Republican donors could spend $750 million on Senate elections this year with no net change.
It may be down ballot where the damage to the GOP could ultimately be more significant. That's because state legislatures will redraw their state congressional maps after the 2020 election.
Since 2008, Democrats have lost more than 900 seats in state legislatures. Cook estimates Republicans could lose five to nine governorships and more than 400 seats in state legislatures this November.
While this class of state legislators won't be the gerrymanders, the next class will be.
Good news may come for Republicans after the election, in Cook's view. Whatever happens in the mid-terms bears no correlation to what happens in the presidential elections.
The Democrats under Presidents Clinton and Obama suffered serious shellackings in 1994 and 2010. Both presidents won re-election with relative ease two years later.
My own guess is that Republicans will perform better than Cook and others think in November. Why? Because older voters, who tend to lean Republican, are more likely to show up in low-turnout elections. Moreover, while the Democrats scored major upsets in a number special elections, they got extremely lucky running respectable candidates against accused child molesters like Roy Moore.