The Chamber of Commerce will back Sen. John CornynJohn CornynAfter Texas shooting, lawmakers question whether military has systemic reporting problem Overnight Defense: Lawmakers question military's lapse after Texas shooting | Trump asks North Korea to 'make a deal' | Senate panel approves Army pick Overnight Regulation: House passes bill to overturn joint-employer rule | Trump officials to allow work requirements for Medicaid | Lawmakers 'alarmed' by EPA's science board changes MORE (R-Texas) in his reelection campaign, helping him in his surprise primary against Tea Party-aligned Rep. Steve StockmanSteve StockmanEx-GOP staffer pleads guilty to fraud, money laundering on behalf of ex-lawmaker Cornyn to run for reelection in 2020 Former congressman indicted on conspiracy charges MORE (R-Texas).

‎"Senator Cornyn is a conservative champion for the American free enterprise system. He has a proven record on issues important to the business community and has received a 90 percent lifetime voting record with the U.S. Chamber," Chamber National Political Director Rob Engstrom said in a statement. "The Chamber is proud to stand with him."

The endorsement is the latest example of establishment conservative and business groups stepping up for Republicans facing right-wing challenges.

The Chamber has also endorsed Rep. Mike Simpson (R-Idaho), a close friend of Speaker John Boehner (R-Ohio). Simpson is facing a Tea Party challenger. Other groups, including former Rep. Steve LaTourette's Republican Main Street Partnership, have promised to spend heavily for centrist candidates.

Stockman, who surprised many with his decision on Monday to run against Cornyn, has not yet received the same support from national conservative groups. The deep-pocketed Club for Growth, the biggest player on the right, said on Tuesday it wouldn't get involved in the race.

Meanwhile, FreedomWorks and the Senate Conservatives Fund have been critical of Cornyn and haven't ruled out involvement in the contest.

Cornyn has nearly $7 million cash on hand for the race, while Stockman has just over $30,000 — and $160,000 in campaign debt.