For all the attention most Texans are expected to pay to it, July 31 is just another Tuesday.

For David Dewhurst and Ted Cruz, it may be one of the most important days of their lives.

By midnight of that day, and probably sooner, Texas Republican voters will find out whether Dewhurst or Cruz will be their party’s nominee to fill Republican U. S. Sen. Kay Bailey Hutchison’s senate seat.

Dewhurst, 66, the Texas lieutenant governor who’s presided over the Texas Senate for almost a decade, several months ago was presumed pretty much a foregone conclusion to win the primary.

But Cruz, 41, the former chief appellate lawyer for Texas Atty. Gen. Greg Abbott, who has never before sought elective office, much less held it, and who thinks compromise is a dirty word, caught fire with the tea party types.

With the help of some Super PACs like the Club for Growth, Cruz has been able to make a decent showing in television ads up against multi-millionaire Dewhurst’s fortune.

Both campaigns have released polls that they say show their guy leading. An independent poll showed Cruz slightly ahead. But in what most likely will be a sparsely attended runoff, it’s anyone’s guess who wins.

If Dewhurst wins the runoff, he then looks forward to the Nov. 6 general election. Particularly in a presidential year, the Republican nominee presumably has a big advantage, since no Democrat has won statewide since 1994.

If Dewhurst wins both those elections, when he vacates the lieutenant governor’s office, the Texas Constitution prescribes that he be replaced by a member of the Senate. The senators will vote among themselves for Dewhurst’s replacement. The only other time that happened – more than 11 years ago – the choice was made by secret ballot.

There’s some question whether Dewhurst’s replacement would be chosen by the outgoing Senate, or the incoming one. That would depend in part on the timing of the vacancy.

The incoming Senate will have at least five new members, and possibly as many as six or seven.

But, should Dewhurst lose Tuesday – election prognosticators say it’s definitely a possibility -- then what?

Will he continue as lieutenant governor? His term doesn’t expire until the third Tuesday of January in 2015. (There’s some grumbling around the Texas capitol at that possibility, from folks ready for a change from Dewhurst’s long and somewhat chilly tenure.)

Or would his disappointment over having his hopes of becoming a 67-year-old freshman senator dashed cause him to quit and do something else, like travel with his younger wife and young daughter, or perhaps spend more time on his team roping hobby?

Might he continue to preside over the Senate, and hope that Gov. Rick Perry doesn’t try in 2014 to add to his already record-setting tenure? That could give the ambitious Dewhurst a chance to run for an open governor’s office – though Atty. Gen. Abbott is also said to be quite interested, and has gradually built up a war chest well over $10 million.

Among political insiders, there’s a continuing guessing game about which senator might become lieutenant governor if Dewhurst does make it to Washington. That speculation will shift into a significantly higher gear after the July 31 election if Dewhurst wins.

In other runoffs that day, Democratic voters will choose between former state Rep. Paul Sadler, 57, and former educator Grady Yarbrough, 75, for their party’s Senate nominee. For Yarbrough, a political unknown with a familiarsounding name, this is his fourth statewide race – twice as a Republican, and now twice as a Democrat. That’s the only statewide Democratic runoff, though there are several others for regional offices.

The Republicans, however, have three other statewide runoffs, and more regional runoffs than the Democrats.

Two are seats on the oiland gas-regulating Texas Railroad Commission, which has nothing to do with railroads anymore, and one is for the Place 4 seat on the Texas Supreme Court.

The hottest and most tightly contested Railroad Commission race is between longtime state Rep. Warren Chisum, 73, R-Pampa, and Christi Craddick, 41.

She has never held elective office. But as the daughter of powerful former Texas House Speaker Tom Craddick, now in his 44th year in the House, six of them as speaker, she has considerable borrowed name identification. And, Tom Craddick, who still has a hefty stash of political campaign cash, has contributed hundreds of thousands of dollars to his daughter’s race, plus called in chits from wealthy donors – to the considerable chagrin of Chisum.

The other commission seat is for the unexpired term of Michael Williams, who quit last year to run for the U.S. Senate, and then switched to a congressional race, which he lost in the primary.

Former Public Utility Commission member Barry Smitherman, 54, is now the incumbent, appointed to the vacancy by Gov. Rick Perry. He got 44.2 percent in the first primary.

That wasn’t enough, in a four-person race, to avoid a runoff. It’s with Comal County Commissioner Greg Parker, 42, who got 27.7 percent.

DAVE MCNEELY is political columnist. You may contact him at davemcneely111@gmail.com or (512)458-2963.