Julian Castro, secretary of Housing and Urban Development under former President Obama, issued a warning to 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) after Democratic candidate Doug Jones won the Alabama Senate race Tuesday.

“Be afraid, @tedcruz . Be very afraid,” Castro tweeted.

Be afraid, @tedcruz . Be very afraid. — Julián Castro (@JulianCastro) December 13, 2017

Jones’s stunning victory over Republican opponent Roy Moore comes after a closely watched campaign to fill the seat vacated by Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE.

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Moore was accused of sexual misconduct last month by multiple women, including one woman who said Moore initiated a sexual encounter with her when she was 14 years old and he was in his 30s.

Moore denied the allegations, but faced calls to drop out of the race from top Republicans.

President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE threw his support behind Moore, however, urging his followers on Twitter to vote for Moore and holding a campaign rally near the Alabama border in support of Moore.

Jones becomes the first Democrat to win a Senate seat in Alabama since 1992.

His victory tightens Republicans’ margin in the Senate, giving them just a 51-49 advantage over Democrats heading into the 2018 midterm elections.

Cruz is facing a challenge from Rep. Beto O’Rourke (D-Texas) in 2018. O’Rourke has raised nearly $2.8 million since he jumped into the race, according to reports filed with the Federal Election Commission.