Updated at 6 p.m. to include candidates for Dallas County Sheriff.

The Dallas-Fort Worth area next year will be the staging ground for the state's most important primary and general elections. From top to bottom, North Texas voters will have a strong say in the makeup of the executive branch and the Legislature.

Most of the contests have already taken shape, but the deadline for candidates to file for office closes at the end of the day Monday, so there could be some 11th-hour moves.

There have already been a number of surprise candidacies. On Friday, Republican Jerry Patterson filed for Texas land commissioner, an attempt to wrestle his old job from incumbent Republican George P. Bush.

On Wednesday, veteran television reporter Brett Shipp launched a campaign for the Democratic Party nomination for the 32nd Congressional District, a seat held by Republican Pete Sessions.

"If you're looking for ground zero of politics for the 2018 cycle, North Texas is it," said Lisa Turner, state director of a Democratic research group called the Lone Star Project. "The area will play an outsize, critical role and is critical to Democrats moving the ball forward in 2018."

Republican consultant Bill Miller said the Dallas area would be the scene of some tough races — and possibly surprises.

"There's some expectation that there won't be many changes, and that could be right," Miller said. "But the smarter expectation is that there could be some surprises in an already interesting election season."

Statewide races

Until Patterson's entry into the land commissioner's race, the Republican primary for statewide offices, including governor, lieutenant governor and attorney general, had a distinct lack of competition. The incumbents face little opposition within their own party.

But Democrats have lined up an array of candidates to challenge the state's top Republicans. Dallas County Sheriff Lupe Valdez is a leading contender for the Democratic Party nomination for governor. The race also includes Houston investor Andrew White, the son of former Texas Gov. Mark White. Valdez needs a big boost from North Texas to propel her candidacy and help down-ballot candidates in the area.

The Dallas area is also important to Rep. Beto O'Rourke, D-El Paso, who is mining votes in Dallas and its suburbs, and even in Republican-controlled Collin County, in hopes of upending incumbent Republican Sen. Ted Cruz in November.

So the 2018 elections will be a test of whether Democrats have closed the gap with Republicans, who have dominated statewide politics for decades.

Congress

Next year is the rare election where Dallas-Fort Worth area congressional seats are in play.

State Sen. Van Taylor, R-Plano, appears poised to win the Republican nomination to replace the retiring Plano Republican Sam Johnson in the 3rd Congressional District based in Collin County. Several Democrats are also vying for the seat, which is considered safely Republican.

But other seats feature crowded primaries.

In the 32nd Congressional District, Shipp joins a field that already includes Colin Allred, Ed Meier, George Rodriguez, Lilian Salerno and Ron Marshall. Sessions is unopposed in the Republican primary.

National Democrats and Republicans have vowed to help their nominees in District 32, which some analysts say could be the most expensive House campaign in history.

Longtime Rep. Jeb Hensarling, R-Dallas, is retiring from the 5th Congressional District, and there's a heated battle to replace him in the GOP primary. Candidates include his former campaign manager, Bunni Pounds of Garland, and former state Rep. Kenneth Sheets of Dallas.

The Republican race to replace Rep. Joe Barton, who isn't running again in District 6 after lewd pictures of him surfaced on the internet, features Ron Wright, J.K. Ellzey and Deborah Gagliardi. Democrats who have filed are Jana Sanchez, John Duncan, Justin Snider, Levii Shocklee and Ruby Faye Woolridge.

Most incumbent members of Congress are not being challenged, with the exception of former state Rep. Barbara Mallory Caraway's fourth consecutive primary battle against longtime District 30 incumbent Eddie Bernice Johnson. Eric Williams is also running against Johnson.

Battle for the Legislature

North Texas is also the scene of several high-profile state Senate races.

In the Collin County-anchored Senate District 8, McKinney educator Angela Paxton is vying against Richardson businessman Phillip Huffines. Paxton is the wife of Attorney General Ken Paxton, and Huffines is the twin brother of state Sen. Don Huffines, R-Dallas.

This contest features two hard-right conservatives and could test loyalties within the party. Paxton has the support of much of the district's conservative political establishment, while Huffines has been campaigning longer and hopes to use his resources and name recognition to mine voters who are not necessarily connected to the Collin County political machine.

The District 8 contest is one of two potentially bruising Senate primaries.

In District 2, Rep. Cindy Burkett, R-Sunnyvale, is challenging incumbent Bob Hall of Edgewood.

Burkett has been endorsed by former state Sen. Bob Deuell, who was defeated by Hall four years ago. Hall is being backed by Lt. Gov. Dan Patrick.

In the Senate District 30 GOP primary, Rep. Pat Fallon of Frisco is challenging incumbent Craig Estes of Wichita Falls in a race that is also expected to be highly competitive.

In Tarrant County, Allison Campolo and Beverly Powell are in a Democratic Party contest for Senate District 10, with the winner meeting incumbent Colleyville Republican Konni Burton in the general election.

Burton, who won the seat after Wendy Davis resigned in 2014 to run for governor, is a major target for Texas Democrats. She's unopposed in the GOP primary.

Democrats have fielded candidates against several Republican House incumbents in Dallas County, part of a strategy to chip away at the Republican majority in the Legislature.

In the Park Cities-anchored District 108, Democrats Joanna Cattanach and Zac Duffy are seeking the nomination, with the winner meeting incumbent Morgan Meyer, R-University Park.

Republican incumbent Jason Villalba is expected to get a primary challenge for House District 114 from Lisa Luby Ryan, who announced her candidacy last month. Democrat and Dallas lawyer John Turner, the son of former U.S. Rep. Jim Turner, is running for the seat as a Democrat.

There are also major challenges from Democrats expected against incumbents Rodney Anderson, Matt Rinaldi and Angie Chen Button.

Republicans Deanna Metzger and Brad Perry are running in the GOP primary for House District 107, with the winner facing incumbent Victoria Neave, D-Dallas, in the always-competitive general election.

In the House District 109 seat being vacated by DeSoto Democrat Helen Giddings, former DeSoto Mayor Carl Sherman and DeSoto council member Deshaundra Lockhart Jones are vying in the Democratic primary.

Dallas County district attorney, sheriff

Former state District Judges John Creuzot and Elizabeth Frizell are tangling for the Democratic nomination for Dallas County district attorney, with the winner meeting incumbent Republican Faith Johnson, who is unopposed in the GOP contest.

Former District Attorney Craig Watkins said Sunday he would not try to regain his old office.

In the race to fill the unexpired term of the outgoing Lupe Valdez, Chief Deputy Sheriff Marian Brown and Dallas County Constable Roy Williams Jr. have filed their candidacies.