Ted Cruz invokes Castro bros, Wendy Davis, to raise campaign funds

Sen. Ted Cruz, R-Tex., addresses delegates during the third day of the Republican National Convention in Cleveland, Wednesday, July 20, 2016. (AP Photo/Mark J. Terrill) Sen. Ted Cruz, R-Tex., addresses delegates during the third day of the Republican National Convention in Cleveland, Wednesday, July 20, 2016. (AP Photo/Mark J. Terrill) Photo: Mark J. Terrill, STF Photo: Mark J. Terrill, STF Image 1 of / 3 Caption Close Ted Cruz invokes Castro bros, Wendy Davis, to raise campaign funds 1 / 3 Back to Gallery

WASHINGTON – Texas Republican Ted Cruz, back in campaign mode after his non-endorsement of Republican presidential candidate Donald Trump, is fundraising off the prospect of a possible 2018 challenge from either U.S. Rep. Joaquin Castro or his brother, HUD Secretary Julian Castro.

A pair of Cruz emails sent out to supporters on Sunday mention both the "Castro brothers" and former gubernatorial candidate Wendy Davis. Joaquin Castro said at the recent Democratic National Convention that he would be "taking a look" at a possible 2018 Senate run.

Davis reportedly told the DNC that she would "see what the future holds."

"These transparent attempts by Texas Democrats to bring the values of Washington D.C. and the party of Barack Obama and Hillary Clinton to The Lone Star State cannot go unanswered," the Cruz team wrote.

It's been more than 20 years since a Democrat won statewide office in Texas, making the prospect of a general election threat to Cruz seem a long-shot, even as Democrats hope to use the 2016 campaign to mobilize and register large numbers of Hispanic voters against Trump.

Joaquin Castro, who represents San Antonio, told reporters at the DNC convention in Philadelphia that he considers a 2018 race "winnable," and suggested that Cruz is "freaked out" over a potential Senate challenge.

Given the hard feelings among many pro-Cruz Texas Republicans for his refusal to back their party's nominee at the GOP convention in Cleveland, some analysts are looking to see whether a GOP primary challenger might emerge as well.

In the face of some GOP critics who considered Cruz's move in Cleveland a betrayal, his campaign is making a direct appeal to party loyalty. "Keep Texas Red," one campaign email said. "Donate today!"