Nate Cohn: “Today’s New York Times/Siena poll finds that the conditions for a so-called wave in November’s midterm elections might be coming into place. The only question is whether — and where — Democrats will be able to ride it.”“Overall, Democrats lead Republicans, 51 percent to 43 percent, among likely voters on the generic ballot question, which asks voters which party they will support for Congress in their district.”“That’s ‘blue wave’ territory. At least in terms of the national vote, the Democratic margin in the poll — 8.5 points — would almost exactly match the party’s 8.6-point margin in 2018. And it would exceed the winning margins for the party out of power in other recent wave elections, like in 1994, 2006 and 2010.”