Democratic presidential candidate Julián Castro, a former San Antonio mayor, hinted that his brother, Rep. Joaquin Castro Joaquin CastroHispanic Caucus members embark on 'virtual bus tour' with Biden campaign Hispanic caucus report takes stock of accomplishments with eye toward 2021 Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-Texas), will challenge Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas) next year.

The presidential candidate was responding to an article from Texas Monthly saying that Joaquin Castro is “all but likely” to run next year against Cornyn, a top Republican in the Senate.

“Looks like I might have some company on the campaign trail soon. I know this: @JoaquinCastrotx would work hard for Texans, not for cozy Washington insiders,” Castro tweeted Saturday.

Looks like I might have some company on the campaign trail soon. I know this: @JoaquinCastrotx would work hard for Texans, not for cozy Washington insiders. https://t.co/nkgtDKxj0k — Julián Castro (@JulianCastro) March 16, 2019

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Matthew Jones, a campaign adviser to Castro, told The Hill that the congressman “will have an announcement in the near future.”

The Texas congressman would be the first high-profile opponent to enter the race against Cornyn, who already boasts former top posts in Congress’ upper chamber and a formidable war chest.

Cornyn’s campaign finished 2018 with nearly $5.8 million on hand, while Castro’s House campaign close the year with $128,000 in its account, according to its most recent filing with the Federal Election Commission (FEC).

Cornyn’s campaign expressed confidence that its candidate would have the upper hand against Castro.

“Whether it’s Hurricane Harvey relief or the Green New Deal, time and again Congressman Castro has stood with Nancy Pelosi Nancy PelosiPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare House lawmakers reach deal to avert shutdown Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE at the expense of Texans,” John Jackson, Cornyn's campaign manager, said in a statement.

“John Cornyn looks forward to contrasting the Democrat-Socialist agenda with the policies that have made Texas the best state to live, work, and raise a family.”

Prospects for Joaquin Castro’s Senate campaign were largely eclipsed by speculation that former Rep. Beto O’Rourke (D-Texas) would decide to take on Cornyn.

But O’Rourke, whose failed Senate bid last year to unseat Sen. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (R-Texas) shattered small dollar donation records and charged the Democratic base, announced this week he would instead run for president.