“Ted is a champion for conservative causes,” said Jeff Roe, Mr. Cruz’s chief strategist. “He’s a champion in Texas and he’s a champion nationally. So I don’t think you should look for him to start straying from his principles.”

A political culture transformed

Republicans have long claimed the pop culture of Texas as their own — the barbecue joints and country music stars and pickup trucks. Mr. O’Rourke embraced those Texas symbols and reclaimed them for Democrats, jamming with Willie Nelson, steering his San Antonio-built Toyota pickup truck through rural Texas and air-drumming post-debate in the drive-through lane at Whataburger. It used to be an awkward counterculture stretch to be a Texas Democrat. He made it cool.

Even before Mr. O’Rourke’s narrow defeat, his yard signs had become one of the biggest visible displays of blue Texas in a generation. His signs easily outnumbered Cruz signs and helped convince the public, the news media and Republicans, long before the polls showed a tight race, that change was coming. It was a mass front-lawn revolt. If you were a Democrat in Texas, the question this fall became: “Where’s your sign?” Up until now, Republicans rarely had yard signs — why bother with a sign when you ruled the state? The strategy on political merchandise is likely to change in the future.

Turning to 2020

There might be a sequel to all this in two years.

John Cornyn, the state’s Republican senior senator, is up for re-election in 2020. Democrats are likely to fire up once again. Will it be Mr. O’Rourke? No one knows for sure.

Mr. O’Rourke failed to turn a well-funded, well-publicized and well-run campaign for Senate into a win. Now, strategists are asking a question: If he couldn’t do it, then who can? And if not now, then when? One of the other Texas Democratic stars — Julian Castro, the Obama-era secretary of housing and urban development — may be booked up in 2020, as he is seriously considering a run for president.

Could even bigger things also be in store for Mr. O’Rourke? He is that rare Texas Democrat whom even Republicans generally have nice things to say about. In the wake of Tuesday’s election, an unlikely voice seemed to be urging Mr. O’Rourke to consider running for president in 2020, even though he has said he’s not interested. That voice belonged to Mr. Roe, Mr. Cruz’s chief strategist.

“I don’t predict Democratic politics, but the fervent following that he has nationally, no one else compares to him on their side,” Mr. Roe told reporters at the Houston hotel ballroom where Mr. Cruz held his victory party. “No one does. He is in a league of his own in the Democratic Party, and if he doesn’t use that to run for president, I don’t know what he’d do with it.”