In 2018, what is a swing state? In many cases, it’s not the spin-off that everyone is focusing on in 2016. How should you optimize your activities and donations? tl; dr: You can donate via PEC ActBlue page (if you like Democrats) either NRSC (if you like Republicans).
The reason for the difference from 2016 is clear: the big question this year is not the President, but who will control the House, Senate, the governors’ palaces and legislatures. In some cases, hot races still take place in the purple states (Nevada, Florida), where statewide voting is tightly divided. But often, perhaps more, regional factors are just as important.
For example, Indiana was very supportive of the Republican party in the presidential vote, but Senator Joe Donnelly (D) defeated the eccentric Richard Mourdock (R) for the Senate seat six years ago in 2012, a Good year for the Democrats. This year, Donnelly has a chance to fight to keep his chair. More broadly, the current polls point to six Senate races: Nevada (D-Rosen v. R-Heller), North Dakota (D-Heitkamp v. R-Cramer), Missouri (D-McCaskill v. R-Hawley), Florida (D-Nelson v. R-Scott), Indiana (D-Donnelly v. R-Braun), and Tennessee (D-Bredesen v. R-Blackburn).
Excluding these races, the Democrats are in favor of finishing with 46 seats, Republicans with 48. To take control, the Democrats will have to win 5 out of 6 competing races. This is a tall order but it is not impossible. Races that look close to this point in the season tend to end in the same direction. For a look at probability, see David Byler’s Senate election model.
Alternatively, one could keep an eye on races in Arizona and New Jersey, although I think Democrats are likely to win both. By contrast, Texas still looks like a Republican organization, at least for now.
Once your donation is done, you can also search for a place to exercise near you. Door-to-door campaigning is by far the most effective way known to increase voters. Swing counties are all over the United States, as you can tell by watching Regional search engine competition 2018.