WASHINGTON – Jeff Sessions wants his old Senate seat back. Standing in his way is not only his strained relationship with President Donald Trump after serving as attorney general, but a host of Republicans who are also vying to go head-to-head with Sen. Doug Jones, the Alabama Democrat who won the seat by a small margin in 2017.

The Senate primary race in Alabama is among several congressional races taking place on Super Tuesday. High-profile races in Texas and California also could have major ramifications for incumbents trying to fend off primary challengers.

Here's a rundown of major congressional primaries taking place Tuesday:

Key Senate races in Alabama, Texas, N.C.

In Alabama, Sessions eked out a victory over six others Tuesday evening, including Roy Moore, the Republican candidate who lost in 2017 against Jones. But it wasn't enough to prevent a runoff election at the end of the month.

Sessions' neck-and-neck race against former Auburn University football coach Tommy Tuberville will continue in a runoff race at the end of the month. In the state, if no candidate wins more than 50% of the vote, the top two candidates will face off in a runoff election.

More:Aides, lawmakers work behind the scenes to try to sway Trump on Jeff Sessions before Alabama Senate primary

In Texas, Republican Sen. John Cornyn fended off a host of Republicans running against him. But he will have to wait a bit longer to learn which Democratic challenger he'll face in November.

The Associated Press declared Air Force veteran MJ Hegar will advance to a runoff race but has not declared who she will face later this month as of 1 a.m. EST.

Her rivals have included state Sen. Royce West, Latina activist Cristina Tzintzún Ramirez, Houston city councilwoman Amanda Edwards and former congressman Chris Bell.

If no candidate gets more than 50% of the vote, the top two candidates will face off in a run off election at the end of the month. The race has piqued national interest due to the massive amount of funding in 2018 that helped Beto O’Rourke come within three points of ousting Republican Sen. Ted Cruz.

In North Carolina, voters decided which Democrat they believe can unseat Sen. Thom Tillis. While Tillis managed to fend off three GOP rivals who were little known statewide, five Democrats were seeking to challenge him in November.

Voters decisively chose former state legislator Cal Cunningham over current state Sen. Erica Smith, according to the Associated Press. Cunningham, an Iraq War veteran and 2010 U.S. Senate candidate, was the leading fundraiser in the primary. He was endorsed by the Democratic Senatorial Campaign Committee and benefited from more than $9 million in outside spending from two super PACs.

Where House incumbents could have trouble

While many incumbents have been able to escape serious primary challengers, a few House members are facing tough battles.

In Texas, one of the most high-profile races being watched nationally is that of Rep. Henry Cuellar, who represents a swath of southwest Texas along the U.S.-Mexico border. He is facing a tough battle against immigration attorney Jessica Cisneros, a progressive whose been endorsed by both Sens. Bernie Sanders and Elizabeth Warren.

The race was still too close to call as of 2 a.m. EST.

The race is also a key test for Justice Democrats, the progressive group that helped elect freshman U.S. Rep. Alexandria Ocasio-Cortez, D-N.Y., in 2018. They are backing Cisneros.

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Another race in Texas was eyed as possible trouble for an incumbent Republican.

Rep. Kay Granger, one of only about a dozen Republican women in the House, was able to fend off a fierce primary challenge against former technology executive Chris Putnam. The Associated Press called the race in Granger's favor shortly before 11 p.m. local time.

She has represented the central Texas district that includes Fort Worth since 1997 and while Trump has backed her, Putnam has posed a serious challenge.

In California, moderate Democratic Rep. Jim Costa faces a more progressive challenger in Esmeralda Soria. The race was too close to call as of 1 a.m. EST.

Costa has served in the House since 2005 and represents the central California district that includes Santa Cruz.

Contributing: Associated Press