He is the best bet now.
December 9th = Last day Democratic or Republican Party candidate may file an application for a place on the primary ballot (6 p.m.). Tex. Elec. Code Ann. § 172.023(a).
http://www.sos.state.tx.us/elections/candidates/guide/dates.shtml
I believe Stockman made the deadline by 15 minutes.
AUSTIN – Congressman Steve Stockman (R-TX 36) announced Monday he is leaving his United States House seat to challenge U.S. Senator John Cornyn (R-TX) for the Republican nomination for U.S. Senate.
“You and I are in a foxhole fighting to save this constitutional Republic, but liberal John Cornyn is bayoneting us in the back,” said Stockman. “Liberal John Cornyn betrayed Ted Cruz and worked with Harry Reid to fund Obamacare.”
“Liberal John Cornyn wakes up every morning and works to make the Senate a more liberal place. That’s why I am running for the United States Senate. I have a 100% pro-gun, pro-life, conservative voting record in Congress,” said Stockman.
“Liberal John Cornyn can’t run on his record, so he will start smearing and attacking me from day one,” said Stockman.
“As my friend Ted Cruz proved, Texans want conservative champions to represent them in the United States Senate. No one has been a more fearless conservative in Congress than I,” said Stockman.
“I stand with my friends Rand Paul and Ted Cruz. Unlike liberal John Cornyn, I will not be Harry Reid’s Republican,” said Stockman.
Stockman’s House withdrawal and Senate candidacy were filed in Austin at 5:59 p.m. CT.
http://stockman2014.com/articles/stockman-challenging-cornyn-for-us-senate