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On the day after this year’s November general election, you’ll know almost everything about how Texas went by knowing how the election went in Dallas County.

It’s a blue county in the most populated red state in the U.S. Hillary Clinton won 60.75 percent of the vote to Donald Trump’s 34.6 percent in 2016. Democrats Wendy Davis and Leticia Van de Putte beat Greg Abbott and Dan Patrick in the races for governor and lieutenant governor in 2014, even as the two Republicans were coasting to easy statewide victories.

Democrats want to keep the Dallas County trend rolling. Republicans, of course, would like to stop it cold.

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This year, the county’s races for the Texas House are the talk of the political class. It’s a blue county. It’s a Republican president’s midterm election. And the seats in question overlap in a stack of contested races from the county courthouse to the statehouse to statewide and federal races.

Dallas is where Democrats hope to pick up the most seats and, conversely, where Republicans are mounting their defenses.

Republicans have majorities in the state’s U.S. House delegation (25-11), the Texas Senate (20-11) and in the Texas House (95-55). In each of those, Democrats hope to pick off Republican incumbents or flip open seats now held by Republicans to their own candidates; Republicans hope to hang on to what they’ve got. As they mapped out their 2018 plans, strategists from both parties found the biggest concentration of competitive seats is in Dallas County, all but one of them with a Republican incumbent:

One Democrat, state Rep. Victoria Neave of Dallas, entered the election year in a district that, like many of those held by Republicans, could swing to the other party. In fact, her HD-107 was on a list like this two years ago, when she defeated Republican state Rep. Kenneth Sheets of Dallas.

Trump lost to Clinton in all of those Dallas districts, and most of the districts have been battlegrounds in each of the last two election cycles. Both parties expect high interest in the race between Republican U.S. Sen. Ted Cruz and Democratic challenger Beto O'Rourke, a congressman from El Paso.

Democrats could get a local boost if former Dallas County Sheriff Lupe Valdez prevails in next month’s Democratic primary for governor against Houston’s Andrew White. Whatever the Democrat’s statewide chances against Abbott, she was elected four times in Dallas County and is better known there than anywhere else in Texas.

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The race for Dallas district attorney is also expected to be a fierce one, featuring Republican Faith Johnson, an Abbott appointee seeking election to that office for the first time, against John Creuzot, who, like Johnson, is a former judge.

It sets up a stack of races that, in some parts of the county, will draw partisans to competitive races from the top of the ballot to the bottom. In a state where Democrats are hoping against recent history for a blue wave, Dallas County has become a potential flood plain. Wins in a significant number of races there could give state Democrats bragging rights even if the Republicans win big in other parts of the state.

The political climate and the sheer number of races could make 2018 a real test of Republicans' ability to hold on and Democrats' ability to make some gains. The county will also have an outsized impact on the overall state results: Dallas is the only part of the state likely to generate much change in the partisan numbers in the congressional or legislative delegations.

The party that wins those Dallas County contests on Nov. 6 will probably have a good day all over Texas.