The Chamber of Commerce will back Sen. John CornynJohn CornynDemocrats up ante in risky debt ceiling fight Senate parliamentarian nixes Democrats' immigration plan Democrats make case to Senate parliamentarian for 8 million green cards MORE (R-Texas) in his reelection campaign, helping him in his surprise primary against Tea Party-aligned Rep. Steve StockmanStephen (Steve) Ernest StockmanPardon talk intensifies as Trump approaches final 24 hours in office GOP senator on Trump pardons: 'It is legal, it is constitutional, but I think it's a misuse of the power' Nothing becomes Donald Trump's presidency like his leaving it 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."

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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.