Voters in Ohio, Indiana, North Carolina and West Virginia will go to the polls to select their nominees for November. A late-stage intra-party fight has President Donald Trump weighing in to stop Don Blankenship's bid for the Republican Senate nomination in West Virginia. By the end of the day, we'll know a lot more about how both parties are selecting their candidates this year as the races take form.

Here's what you need to know:

Indiana

CLOSEST TO TRUMP: Indiana's Republican Senate primary boasts a highly competitive three-way race. US Reps Luke Messer (IN-06) and Todd Rokita (IN-04) -- whose personal rivalry began at the same small college decades ago -- are battling businessman Mike Braun, who has run as an outsider and is largely self-funding. The race has been a battle of who can be the most dedicated Trump supporter and exemplifies the extent to which the Republican party has coalesced around their president. The winner of Tuesday's primary will take on incumbent Democratic Sen. Joe Donnelly in November, in the state that voted for Trump by 19 points in 2016.

PENCE BACK IN THE HOUSE: Vice President Mike Pence's older brother Greg is running for the GOP nomination in the 6th district. His brother served in the House from 2001-2013.

Ohio

PENNSYLVANIA OR ARIZONA?: Ohio's 12th district will hold primaries for the August 7th Special Election to replace former Rep. Pat Tiberi, who resigned in January to lead the Ohio Business Roundtable. The race was seen as long shot a few months ago, but the special election win in Pennsylvania, and a close race in Arizona, could give the Democrats another chance to flip a House seat before November.

West Virginia

TRUMPIER THAN TRUMP: Like Indiana, Republicans here are trying to out-Trump Trump. Rep. Evan Jenkins is battling Attorney General Patrick Morrisey and ex-convict Don Blankenship, former CEO of Massey Energy Co. In the final days of the primary campaign, Blankenship made multiple racist attacks against Senate Majority Leader Mitch McConnell's father-in-law. While Jenkins and Morrisey did not use such personal attacks, both of them said they would not support McConnell as the next Republican Senate leader. President Trump urged West Virginia Republicans to avoid supporting Blankenship, and vote for either Jenkins or Morrisey, in the hopes of avoiding another upset ala Doug Jones over Roy Moore in Alabama. Whoever emerges from the primary will take on Manchin, another vulnerable Democratic incumbent. Trump won the state by more than 40 points in 2016, but Manchin -- a former two-term governor -- hopes his moderate views and history with the state will keep him in office.

North Carolina

DEMOCRATS ON THE RISE?: Three Republican-held seats will be important to watch in North Carolina: Reps. George Holding, Robert Pittenger and Ted Budd all won re-election in 2016 with at least 55% of the vote. Should Democrats turn out and nominate viable candidates in these seats, it will help put them at risk in the fall, and potentially expand the already wide field of competitive House seats in November.