Washington (CNN) This year's midterm elections officially kick off Tuesday with the Texas primaries, where voters will sift through jam-packed fields of Democratic candidates vying to take on vulnerable Republican members of Congress.

Here's what you need to know:

Here's a closer look at the six races to watch tonight:

Family legacy on the line: Incumbent Texas Land Commissioner George P. Bush -- the son of Jeb Bush and the last Bush in political office -- faces a primary challenge from former land commissioner Jerry Patterson. This is a race over the Alamo: Patterson has campaigned against what he calls Bush's failed stewardship of the site of the historic battle.

Progressives vs. Establishment: It was already a bare-knuckled brawl among the seven Democrats vying to take on Republican Rep. John Culberson in Texas' 7th House District. Then the Democratic Congressional Campaign Committee got involved, dropping a bomb on one of the candidates, Laura Moser,a candidate backed by Bernie Sanders' allies, and turning the race into something of a proxy for the larger war within the party. Emily's List-backed lawyer Lizzie Pannill Fletcher and attorney Alex Triantaphyllis are other candidates to watch in a race that could be headed for a runoff.

Take a closer look at that race here

Border district brawl: Party figures have split over this contest to take on GOP Rep. Will Hurd in the 23rd House District between Iraq War veteran Gina Ortiz Jones, former federal prosecutor Jay Hulings and former Agriculture Department official Judy Canales.

Democrats fight for Dallas: The third competitive Republican-held seat in Texas' 32nd District is represented by Republican Pete Sessions. The Democrats vying to replace him are former NFL player and attorney Colin Allred, former Agriculture Department official Lillian Salerno and former State Department official Ed Meier.

Who will take on Abbott: Senate candidate Beto O'Rourke, running to oppose Republican Sen. Ted Cruz, is the statewide headliner for Democrats this cycle. But Republican Gov. Greg Abbott is up for re-election as well, and former Dallas County Sheriff Lupe Valdez and businessman Andrew White are vying to take him on.

An interesting split: The campaign to replace retiring Rep. Gene Green in the reliably blue 29th District has seen an interesting split between Senate Minority Leader Chuck Schumer, who is backing Tahir Javed, and Emily's List and the other New York senator, Kirsten Gillibrand, who are backing state Sen. Sylvia Garcia.

CLARIFICATION: This story has been updated to reflect poll times in the El Paso area.

CORRECTION: This story has been updated to correctly identify state Sen. Sylvia Garcia.