Stockman has missed 17 straight House votes since Jan. 9- including one on the $1.1 trillion omnibus federal spending package he promised on Twitter to vote against. That's unusual since, even though Stockman has a reputation as a Capitol Hill renegade, he missed only about a dozen major votes all last year.
The disappearance is mystifying for conservative activists who were hoping Stockman could help them land another blow against the GOP establishment this year. Texas has been a showcase for the right wing's power since firebrand Ted Cruz rose from back in the party's ranks in 2012 to become a U.S. Senate sensation.
But Stockman's challenge has slipped from quixotic to downright unusual.
"He thought he was another Ted Cruz and he isn't," said William Murray, chairman of the Washington-based Government is Not God PAC, which backedStockman's congressional campaigns in the 1990s and 2012 but has now endorsed Cornyn.
Once a homeless college dropout, Stockman is a born-again Christian who lists his official occupation as "Constitutionalist." He served one term in Congress beginning in 1994, then returned last year and has attracted attention in conservative circles with flamboyant rhetoric about impeaching President Barack Obama and promoting gun rights. Stockman even had a copy of the book "Impeachable Offenses: The Case for Removing Barack Obama from Office" hand-delivered to all 435 House members.
After first dropping out of sight, the congressman recently was spotted on a visit to Egypt as a member of the House Foreign Affairs Committee - but where he's gone since then is unclear.
Stockman's staff won't say where he is. They have ignored more than six weeks of emails, telephone messages and social media posts from The Associated Press and other news outlets.
Cornyn, seeking his third term, has a campaign that's been more responsive: "It's up to Texans to decide if they think someone who doesn't show up to work or adhere to election law deserves a promotion," said spokesman Drew Brandewie.
Though skipping votes isn't uncommon for congressmen who are campaigning, Stockman hasn't done much campaigning, even with Texas' March 4Republican primary now looming.
Since suddenly withdrawing his bid for re-election to his House seat and filing against Cornyn on Dec. 9, Stockman has made just one major public appearance in Texas- chastising Cornyn as too liberal before about 50 tea party activists at a north Dallas church Jan. 14. That followed his skipping a scheduled appearance before a larger tea party group in Bedford, near Fort Worth.
Dale Huls, a board member of the Clear Lake Tea Party in Stockman's district, said the congressman has been quietly courting conservative organizations and local grassroots activists. Still, he called Stockman's campaign "a little chaotic."
"I would expect a more transparent staff to citizens and tea party groups," Huls said.
Stockman's problems go beyond visibility. He has reported having only about $32,000 in cash on-hand and $163,000 in debts, while Cornyn's campaign fund is nearly $7 million.
Murray, of the Government is Not God PAC, said he got a call soliciting donations for Stockman but "I was so furious he was throwing away that congressional seat, I dressed them down pretty good."
The anti-tax Club for Growth has shunned him - after spending around $5.5 million to help Cruz upset mainstream Republican contender David Dewhurst in the state's 2012 U.S. Senate GOP primary.
Since making it back to Congress, Stockman has thrived on shock-value publicity, claiming "Democrats worship abortion with the same fervor the Canaanites worshipped Molech" and offering supporters a campaign bumper sticker reading, "If babies had guns, they wouldn't be aborted." A Stockmancampaign website suggesting that Cornyn secretly supports the White House-backed health care law even doctored what appears to be an old picture of then-Florida Gov. Charlie Crist beaming at the president to make it look like Cornyn was the one doing so.
But investigations by The Houston Chronicle and the watchdog Sunlight Foundation have uncovered a bevy of potential violations of Federal Election Commission rules. In October, Stockman fired two congressional staffers for making prohibited contributions to his campaign.
Some tea party groups maintain that Stockman can still rally. "I know that Steve has gotten hit from multiple sides," said Larry Ward, political director of the Revolution PAC in Washington, "but that wouldn't be happening if he weren't a serious threat."