Some quick analysis of the 2019 off-years:
Kentucky: Obviously a huge win for Rand Paul, as one of his proteges in the House knocks off a sitting Democratic Governor in his home state a mere two-and-a-half months before Iowa. It's a big win for his brand of libertarian conservatism, too, in that no Paulite Governor has ever been elected before. Massie's campaign was one based largely on conservative platitudes and borrowed heavily from the statewide infrastructure in place from both sitting Senators, and was backed by the coal industry and large outside groups including both the Koch network and more establishment-oriented figures. With the KY House still run by Democrat Greg Stumbo, how much of Massie's agenda can be passed is unclear.
Louisiana: The budget mess left over by Bobby Jindal continues to haunt David Vitter, who despite a competent, low-controversy first term is still hobbled in his attempts to make Louisiana a more competitive state and prevent the continued out-migration by rural and suburban whites. Democrats capitalize on frustration with the state's leadership, and despite not dislodging any of the statewide officeholders make gains back with old-fashioned Blue Dogs in Acadiana-area seats and in term-limited safe seats elect a swath of young, liberal legislators for the most part under the age of 40. The question asked by many, including the influential Landrieus, is whether this bench can be competitive in future statewide elections and where exactly they're going to go with Cedric Richmond showing no signs of retiring.
Mississippi: Outside of Jim Hood, indestructible as always, Republicans continue to press their majority in America's most conservative state. The competent, likable Tate Reeves wins a landslide and carries the GOP into even larger majorities in both houses of the state legislature. Good feelings in the sports-obsessed state over Ole Miss' national championship and an Elite Eight run by the Mississippi State basketball team are said to help the incumbents, too. Reeves outlines a program to bring manufacturing, research and "21st-century jobs" to the economically suffering state, indicating a much more ambitious approach to governing than his ardently small-government predecessor showed.
New Jersey: Dual frustrations collide in New Jersey to cost the Democrats - an inability to fix the massive budget mess left by Chris Christie in quick fashion, tax hikes across the board, teacher's strikes, defaults by three municipalities and a poor economy. Steve Fulop gives a press conference accepting the results of the election and promises to work to make the state more competitive. It should be noted that despite losing ten seats Democrats still control the House by a healthy margin, so policy-wise the results are not a disaster, but local Dems are still worried that the young, less-than-charismatic Fulop might be in over his head and see a Tom Kean run in 2021 as potentially disastrous for the party.
Virginia: The opposite effects are odd in Virginia - Dick Black was obviously no longer acceptable to his diversifying district and the Hampton Roads-area successor to Frank Wagner, retired Commander John Angier (fictional), was surprisingly strong. Virginia's strong economy and decently popular Governor Herring was not enough to take care of incumbents in gerrymandered House districts in an off-off-year election that beefs up the Democratic majority in the Senate to avoid Lt. Gov. Perriello's need for a tiebreaker and yet strengthens the Republican grip on the House of Delegates. A status quo election for the ages.