Tuesday brings the busiest primary day of 2018 thus far, with voters in four states going to the polls to choose party nominees for the November 6th midterm elections. Republicans in three of those states, all won easily by Donald Trump in 2016, will choose nominees to face off against Democratic Senate incumbents.

Polls in North Carolina, Ohio and West Virginia will close at 7:30 PM Eastern Time. In Indiana, polls close at 6:00 PM local time. That's 6:00 PM Eastern for most of the state; 7:00 PM Eastern for the sections in the Central Time Zone.

A summary of the three Senate races follows.

West Virginia: This race has been getting the most attention in recent days, as former coal executive Don Blankenship has moved to be "Trumpier than Trump" in an effort to defeat two establishment opponents. His effort includes a campaign ad that won't soon be forgotten:

President Trump tweeted that Blankenship can't win in November, telling voters to choose one of his two opponents, Rep. Evan Jenkins or Attorney General Patrick Morrisey. 'Two' is the problem here for the GOP. It is entirely possible that those two split the mainstream vote while Blankenship wins a plurality. That scenario would significantly brighten the re-election prospects of Sen. Joe Manchin in a state Trump won by 42% in 2016.

Indiana

Three Republicans are also competing for the nomination in this state that Trump won by 19%. Reps. Todd Rokita and Luke Messer don't like each other, although they and former state lawmaker Mike Braun all really like the president. The winner of today's primary will face incumbent Sen. Joe Donnelly.

Ohio

Trump won Ohio by 8% in 2016. While a more competitive result than West Virginia or Indiana, it was the largest presidential margin of victory in that bellwether state since George H.W. Bush beat Michael Dukakis by 11% in 1988. Rep. Jim Renacci is squaring off against banker Mike Gibbons and several others. All recent polling is like this one: Renacci is ahead but with a huge amount of undecided voters. The winner will meet incumbent Sen. Sherrod Brown.

Upcoming Primary Calendar

Aside from Memorial Day week, the next month will be very active. Here's the full calendar.

May 15:  Idaho, Nebraska, Oregon, Pennsylvania

May 22:  Arkansas, Georgia, Kentucky

June 5:   Alabama, California, Iowa, Mississippi, Montana, New Jersey, New Mexico, South Dakota

June 12:  Maine, Nevada, North Dakota, South Carolina, Virginia