Now we may have a nice, clean test case for the “big or merely loud” conversation about the insurgents in the Texas Republican Party.

If they’re big, U.S. Sen. John Cornyn is in trouble.

If they are merely loud, Steve Stockman, who is giving up a chance at re-election to the U.S. House to challenge Cornyn, will lose convincingly, and the establishment can sit back and enjoy a cigar and a brandy.

Stockman is a piece of work — a quotable renegade who has been upsetting establishment types for years. He embodies what the mainline Republicans think of the noisy populists in their midst.

Cornyn does the same thing for the populists. He came up through the ranks as a judge, a state attorney general and then a senator. He took the lead in the Senate for former President George W. Bush’s initiatives there.

Stockman wants to be the next Ted Cruz. Cornyn wants not to be the next David Dewhurst.

That Cruz-Dewhurst match will not be replayed here. Stockman doesn’t have time to run the race that Cruz ran in 2012, with scores of appearances at town halls, civic clubs, luncheons, dinners, pachangas and barbecues all over the state.

And he may not have the same level of support, even from the hard-liners. The third-party groups that fueled the Cruz missile are busy in other races in other states, where it is cheaper to run campaigns and where the targets are more attractive than Cornyn.

For all of the talk about Cruz not endorsing Cornyn, there is another and more important silence that has gone unnoticed: Cruz has not endorsed Stockman.

Cruz opposing Cornyn would be a big talking point. But Cruz supporting Stockman could be transformative. He is the Good Housekeeping Seal for his branch of the party. Without it — or something similarly strong — Stockman is just another congressman trying to take out a senator.

That said, Stockman’s candidacy is also a high-stakes bet on the side of the populists, or Tea Partyers, or whichever label suits you. Cornyn is hardly a liberal, but he didn’t support Cruz 100 percent on the government shutdown and health care standoff. The purists want a change, and Stockman turns out to be their best vehicle.

Stockman made his opening argument in a Twitter message: “Unlike liberal John Cornyn, I will not be Harry Reid’s Republican.”

Maybe he is not the best standard-bearer. He’s not exactly former U.S. Rep. Ron Paul or Cruz. He is not as well known and not as careful about picking his political targets.

He is often portrayed as a loon, particularly by talkers and writers on the left. In the wake of Stockman’s surprise switch from a re-election race to a Cornyn challenge, they mustered their favorite Stockman moments — the candidate’s idea for a campaign bumper sticker (“If babies had guns, they wouldn’t be aborted”) and the comparison of the Senate to the mob that called for the crucifixion of Jesus.

The congressman has a hard road ahead. The election is close. It is less expensive to win a Senate seat in a small state than in a big one, and the political money flows accordingly. Stockman would have a hard time raising national money even without that competition, and he would first have to show that Cornyn was vulnerable. That is iffy at best.

Time is also his enemy. By waiting until the end of the filing period, Stockman entered the race just 10 weeks before the start of early voting in the primaries. He has to introduce himself, distinguish himself, raise and spend the money to accomplish those ends in less than three months, and do it all around the obstacles of the holidays and the bowl games and the Winter Olympics.

The challenger is carrying a load on his back. The same Republicans regularly asking why the Democrats think they have a snowball’s chance in next year’s elections might well be asking the same question of their fellow Republicans.

The insurgents have made a lot of noise, developed a commanding presence in social media and scared the stuffing out of their establishment colleagues. Do they have the votes to back up the talk?