Uncertainty hangs over Texas as voters head to the polls this Election Day

It's been a long while since Texas entered an Election Day with so much uncertainty hanging over it.

From the blockbuster matchup at the top of the ballot between U.S. Sen. Ted Cruz, R-Texas and U.S. Rep. Beto O'Rourke, D-El Paso, to a bevy of potentially close races further down the ballot, predictions of what the results will look like after polls close Tuesday evening are all over the place.

The flood of early voting has scrambled all historical precedent, and what happens on Election Day could reset — or reaffirm — the trajectory of Texas politics.

"The enthusiasm is absolutely real," said Harris County Democratic Chairwoman Lillie Schechter. "Our statewide polling and now our turnout demonstrates that Democrats all over the state are not happy with the Republican leadership and are demanding changes."

But Brendan Steinhauser, a Republican consultant with several clients on the ballot on Tuesday, suggested that some of that surge in early turnout was of a Republican bent. Either way, Republicans are taking nothing for granted.

"Everyone's on the same page in that they're taking every race up and down the ballot seriously," he said. "Everybody's sprinting through the finish line in a way that I haven't seen since I've been working elections here."

"I think there's a sense of mixed hope and consternation," he added. "The numbers we see coming back in internal polling, in public polling and county-by-county data is ... that people are fired up to vote. We're seeing it on the Democratic side and the Republican side."

At the center of Texas politics is the U.S. Senate race between Cruz and O'Rourke. Cruz has led in nearly all of the polling and has the structural advantage. But many political insiders wonder if O'Rourke, with the eye-popping $70 million in donations he's attracted to his bid amid political rallies that have drawn crowds more akin to rock concerts, has so expanded the electorate that a path exists for a Democrat to win a U.S. Senate race for the first time since 1988.

Geographically, the race is on track to test the clout of the state's fast-growing urban centers. Should Cruz survive, much of that success will likely be rooted in more rural communities.

The most closely watched county of all is likely to be Tarrant County, the last large urban Republican stronghold in the state. If Tarrant flips for O'Rourke, it could be a new day in Texas politics.

Aside from O'Rourke's muscular challenge for U.S. Senate, much of the remaining statewide ballot has been far quieter. Gov. Greg Abbott, for instance, has enjoyed double-digit leads against Democrat Lupe Valdez, the former Dallas County Sheriff, in some polls, and is putting much of his campaign infrastructure toward helping boost Cruz and others in tougher races. Texas Attorney General Ken Paxton has also run a mostly under-the-radar re-election campaign against Democrat Justin Nelson, but a burst of new ads and large last-minute donations to Paxton's campaign in the final days suggest Republicans aren't taking that race for granted amid such a volatile environment.

Down ballot, there are three congressional races that are the most closely watched, in Dallas, Houston and West Texas. In all three districts, more voters backed Hillary Clinton over Donald Trump in 2016, while also re-electing the GOP incumbents in the U.S. House. U.S. Rep. Pete Sessions is in a high-profile battle against attorney Colin Allred in North Dallas' 32nd District. In Houston, Republican U.S. Rep. John Culberson is deadlocked against Democratic attorney Lizzie Pannill Fletcher in the 7th Congressional District.

There is more confidence in the GOP world that U.S. Rep. Will Hurd is on the march to a third term, despite efforts by retired Air Force intelligence officer Gina Ortiz Jones to unseat him. Yet late last month, the National Republican Congressional Committee was back on TV in the district after canceling reservations there weeks earlier, a sign that national Republicans remained worried about the race.

Elsewhere, Democrats are expected to run up the score in the state's two largest counties — Harris and Dallas — and there could be serious down-ballot consequences as a result.

"We have always said that growing our electorate to grow our power is a long term project and every cycle that we add Democrats to the electorate is a successful election and a step in the right direction," Schecter said.

Sleeper races could emerge on the congressional front as well, given the robust fundraising of Democratic challengers across the state.

Beyond the statewide and congressional match-ups, three races in GOP-dominated state Senate seats have also generated interest, with some Republicans worried that Lt. Gov. Dan Patrick could lose his stronghold on the upper chamber should those seats flip. In Senate District 16, incumbent Don Huffines and Democrat Nathan Johnson are fighting to see who will represent a district in Dallas County that has been represented by a Republican for more than three decades.

What’s working to Johnson’s advantage is an obvious fanfare for O’Rourke and the fact that Senate District 16 overlaps with the 32nd Congressional District, where recent polls show Sessions trailing Allred by single digits. The district also supported Clinton over Trump by nearly 5 percentage points in 2016.

A similar situation is unfolding in state Senate races in Tarrant County and the Houston-area, where Republican state Sens. Konni Burton and Joan Huffman, respectively, are vying for re-election. Burton, a Colleyville Republican facing a challenge from Democrat Beverly Powell, will have to navigate a historically competitive re-election bid. In 2014, she flipped the seat from Democrat Wendy Davis with a little more than 52 percent of the vote. Two years later, Trump beat Clinton in the district by only half a percentage point. In Huffman’s district, Trump won by less than one percentage point.

Further down the ballot, there are several state House seats in play. Dallas County in particular has been a central battleground for several Democrats running aggressive campaigns against incumbent Republicans. If a “blue wave” does overwhelm the area, Democrats are hopeful more than a handful of seats will flip in their favor, including ones currently held by state Reps. Matt Rinaldi of Irving, Rodney Anderson of Grand Prairie, Angie Chen Button of Richardson and Linda Koop and Morgan Meyer, both of Dallas.

Two open state house seats in the Dallas-area could flip toward Democrats as well. The House District 114 race in Dallas County will determine who will succeed Republican state Rep. Jason Villalba of Dallas, a relatively moderate three-term legislator who lost his GOP primary earlier this year. Politicos are also keeping an eye on the neighboring House District 113, where Democrat Rhetta Bowers and Republican Jonathan Boos are vying for the seat vacated by state Rep. Cindy Burkett.

In Williamson County, too, several legislative seats are in play. Democrat James Talarico and Republican Cynthia Flores are duking it out to replace the retiring state Rep. Larry Gonzales, R-Round Rock. In a neighboring district, state Rep. Tony Dale is hoping to hold his seat against Democrat John Bucy.