Former Indiana state Rep. Mike Braun, right, and Rep. Todd Rokita, speaking, are running for the GOP nomination for Senate, along with Rep. Luke Messer. (Tom Williams/CQ Roll Call file photo)
Tuesday marks the first big primary day of 2018. Voters go to the polls in Indiana, Ohio, West Virginia and North Carolina.
Most of the exciting action is on the Republican side. In all of those states (except for North Carolina), Democratic senators are trying to hold on to seats in territory President Donald Trump won in 2016, which means the GOP primaries are high-stakes contests. (More on that below.)