Influential conservative group endorses Ronny Jackson over Josh Winegarner in runoff for U.S. Rep. Mac Thornberry's seat

The Club for Growth is taking sides in one of the highest-profile Republican primary runoffs this summer in Texas.

The deep-pocketed national conservative group is endorsing Ronny Jackson, the former White House physician, to replace retiring U.S. Rep. Mac Thornberry, R-Clarendon, in his safely Republican district. Jackson has the support of President Donald Trump in the July runoff against Thornberry's preferred successor, Josh Winegarner.

"We are proud to join President Trump in endorsing Ronny Jackson, a principled, pro-growth conservative and former presidential physician who served our country in uniform as an admiral in the U.S. Navy," Club for Growth's president, David McIntosh, said in the group’s endorsement, which was first shared with The Texas Tribune.

The Club for Growth previously endorsed Chris Ekstrom, a prominent anti-establishment GOP donor, in the 15-way March primary. He finished third and has since thrown his support to Jackson as well.

Winegarner, industry affairs director for the Texas Cattle Feeders Association, came in first in the primary, getting 39% to Jackson's 20%. Since then, the runoff has seen a slew of endorsements split between Jackson and Winegarner.

Jackson has picked up runoff endorsements from several statewide conservative groups like Texas Right to Life, as well as a couple of veterans groups and Agriculture Commissioner Sid Miller. Winegarner, meanwhile, has added endorsements from prominent GOP figures from West Texas and the Panhandle, including state Sen. Charles Perry of Lubbock and his predecessor, Robert Duncan; former U.S. Sen. Phil Gramm, for whom Winegarner once worked; and Tom Mechler, the former Texas GOP chairman.

On Friday, Jackson rolled out the endorsement of U.S. Rep. Steve Stivers of Ohio, a fellow veteran who served as the chairman of the National Republican Congressional Committee during the 2018 election cycle.

However, easily the most important endorser in the race has been Trump, who sent out a tweet a few days before the March primary urging voters to send Jackson to the runoff. Trump weighed in again Friday, tweeting that Jackson has his "Complete and Total Endorsement."