(Bloomberg) -- John Thune, the second-ranking Republican in the US Senate, has endorsed former President Donald Trump in his bid for the White House.

A spokesperson for Thune on Sunday confirmed the senator will throw his support behind Trump for the Republican presidential nomination. Thune, of South Dakota, spoke by phone with Trump after his win over Nikki Haley in the South Carolina primary. 

Fox News first reported the endorsement.   

The endorsement is the latest indication that establishment GOP members are falling in line behind Trump as he seeks a second term in the White House and a re-match against President Joe Biden in November. 

Thune had previously resisted joining Trump’s allies and has questioned the GOP front-runner’s strength as a general-election candidate. He had originally backed Senator Tim Scott of South Carolina as the Republican candidate.

Thune, the minority whip, is widely seen as a potential successor to Minority Leader Mitch McConnell whenever that job opens up. His endorsement of Trump comes after two other leading candidates to replace McConnell, Senators John Cornyn of Texas and John Barrasso of Wyoming, recently signed on.

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