Voters head to the polls Tuesday in Texas for an intriguing slate of runoff elections with far-reaching implications.

Polls close at 8 p.m. ET. We'll have results for you this evening on Post Politics. For now, these are the five biggest things to watch:

1. Will the oldest member of Congress survive a tough primary challenger?

At 91, Rep. Ralph Hall (R) is the oldest member of Congress. But if he is going to win another term, which he says would be his last, he will have to get past former U.S. attorney John Ratcliffe, who is more than four decades younger. Age has been a central issue in the campaign, with Ratcliffe not-so-subtly reminding voters of Hall's age in one of his commercials and Hall poking fun at his wrinkles in one of his own ads. National tea party groups have lined up behind Ratcliffe, but the contest has been more generational than ideological, close observers say. Hall appears to have the upper hand entering Election Day, but he's far from a sure bet. "I think Hall is reasonably good shape, but he certainly is not out of the woods," said Rice University political scientist Mark Jones.

2. David Dewhurst's last stand 

It wasn't too long ago that Lt. Gov. David Dewhurst (R) was widely regarded as the next U.S. senator from Texas. But Ted Cruz defeated him in a stunning 2012 primary upset and then won the Senate seat, and things only got worse from there for Dewhurst. He is widely expected to lose the runoff election for the job he holds to state Sen. Dan Patrick (R), who is running to Dewhurst's right. Democrats are excited about the prospect of facing the more conservative Patrick in the general election since they have highly touted state Sen. Leticia Van de Putte as their standard-bearer. Still, Patrick would be favored in the general election.

3. Who will Republicans nominate in the state's one swing congressional district?

Former congressman Francisco "Quico" Canseco (R) is vying for a second straight run against Rep. Pete Gallego (D) in the only swing district in the state. But former CIA officer Will Hurd (R) is a real threat in the runoff. "That's going to be a very tight race. Hurd is looking a little better," headed into the election, said Jones. Regardless of who wins, Gallego looks a lot safer than he did a few months ago. He will begin the race to November as the favorite no matter what.

4. The Ted Cruz connection 

In the GOP runoff for attorney general, state Sen. Ken Paxton is the frontrunner. In a TV ad, Paxton has touted the praise (if not an official endorsement) Cruz has given him and is clearly running as a tea party candidate in Cruz's mold against state Rep. Dan Branch. In the GOP runoff for the state Senate seat being vacated by Democratic gubernatorial nominee Wendy Davis, Cruz is supporting tea party activist Konni Burton, who Jones says he expects will win the nomination.

5. The Democratic primary for U.S. Senate

Regardless of what happens, Sen. John Cornyn (R) will be a heavy favorite to win in the fall. But for Democrats talking about competing statewide in Texas, it would be an embarrassment if they could not shepherd establishment-backed wealthy dentist David Alameel past underdog Kesha Rogers, who thinks President Obama should be impeached. Alameel is expected to win, but keep an eye on what percentage of the vote Rogers receives for a measure of the discord in Democratic circles right now.