The rash of recent retirements by House Republicans along with the decisions by a number of top-tier Republicans being courted to run for the Senate combine to reinforce the view that many of us have had for months— it sure looks like there will be Democratic wave crashing down on the GOP in the November midterm elections.

Just this week, Rep. Ed Royce’s announcement that he would not seek re-election in a district that he last won by 21 points but that Hillary Clinton won by eight points was a tough blow for the GOP. Fellow California Rep. Darrell Issa’s decision to bail out is somewhat less of a blow to the party, as Democrats had a good chance of knocking him out if he did run again. Issa won by less than 1,700 votes in a district Clinton won by seven percentage points. And the announcement by Rep. Kevin Cramer that he would not challenge Democratic incumbent Heidi Heitkamp in North Dakota means that Senate Republicans will have to go with a second- or third-tier contender against her in what was supposed to be one of their top targets. When a party seems to be under siege, the old Morton’s Salt advertising slogan comes to mind: “When it rains, it pours.” Bad news snowballs.

A key question for November is which will be dominant: the environment or geography. Put another way, in both the House and Senate, it’s the wave versus the map.

While congressional district boundaries and natural population patterns of Democrats being more concentrated in urban areas can be expected to partially mitigate the impact of a wave, the operative word is partially. And at least today, the wave looks awfully powerful. A combination of historically low presidential job approval ratings, terrible generic congressional ballot test numbers for the GOP, results in last year’s elections and an enthusiasm deficit among GOP voters all point to something big. Just about any fair-minded assessment of the House would show that Democrats have probably more than a 50-50 chance of taking control of the House.

But the map is much tougher in the Senate for Democrats. Statistics maven Nate Silver makes the case strongly on his FiveThirtyEight website this week, quantifying the challenge that Democrats face given the seats they have to defend themselves and the ones they need to take away from the GOP. Pointing to prediction markets that put Democratic chances of winning Senate control as high as 45 percent, Silver doesn’t that it can’t or won’t happen, just that such talk is currently premature.

It should be pointed out that Silver and I look at many of the same things but from different perspectives. Silver—a very smart guy who started out as one of the top statisticians analyzing baseball data before branching out to become a real authority on elections—approaches things from the quantitative side. My background is more on the qualitative side, watching the numbers but taking a lot of non-numerical points into consideration as well. A baseball analogy: Every major-league team now employs at least one or even a team of statisticians to comb through the data, but not one has fired all of their old-fashioned scouts. The best approach is more of a hybrid, combining elements of both approaches, as we are increasingly trying to do at the Cook Political Report.

In Silver’s piece he performs an interesting exercise by taking the latest ratings from the Cook Political Report and Larry Sabato’s University of Virginia-based, invaluable Crystal Ball as well as those of Inside Elections, an excellent newsletter produced by Nathan Gonzales (started by Stu Rothenberg over 30 years ago). FiveThirtyEight then converts the ratings by each publication into numbers, then crunches the data, playing out various scenarios by changing assumptions. Which assumptions one employs makes all the difference in the world—one scenario gives Democrats just a one percent chance of capturing a Senate majority, while the other extreme puts it at 50-50. Silver dubs both as unrealistic, with the real odds somewhere in between. The key is how you think the races rated as “toss up” break, and it’s important to note that they rarely split evenly; instead they tend to break strongly one way or the other, especially in wave years.

Closely comparing the various ratings reveals nuances in our different approaches. Take the Florida Senate race, where Democrat Bill Nelson is seeking re-election. Sabato’s Crystal Ball puts the race as a Toss Up while Gonzales’s Inside Elections and the Cook Political Report label it as Lean Democrat. Republican Gov. Rick Scott is widely expected to take Nelson on, with polls already showing the race a dead heat. I can’t speak for Gonzales but at Cook, our policy is pretty much not to assume anyone’s candidacy until they’re definitely in; if Scott does run, Senior Editor and Senate specialist Jennifer Duffy would likely change the rating to Toss Up instantaneously. We often see candidates take a pass whom we’d assumed would run, and we cautiously prefer to avoid frequent ratings changes.

If someone said that Democrats had a one-in-five, one-in-four or a one-in-three chance of taking back the Senate, that seems about right for what we know right now. The real outcome will depend upon a lot of different factors, both secular events in each race and the national environment. Does our currently strong economy continue into next fall? Will President Trump begin to get more credit for it than he does now? Will he be an anchor weighing down Republicans and if so, how heavy will that anchor be? The closer we get to the election, the better sense we’ll have of whether the wave or the map is winning out.

This story was originally published on on January 13, 2018

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