Report: Romney to endorse Rubio

Former GOP presidential nominee Mitt Romney will endorse Marco RubioMarco RubioHaley to meet with senators during Washington trip Senate GOP to Obama: Stop issuing new rules Juan Williams: McConnell won big by blocking Obama MORE’s White House bid, The Huffington Post reported early Sunday.

The news outlet cited two unidentified sources who said Romney withheld his high-profile endorsement out of respect for Jeb Bush, who ended his campaign late Saturday after a disappointing fourth-place finish in South Carolina primary.

Rubio edged fellow freshman senator Ted Cruz for second place in the Palmetto State, behind Donald TrumpDonald TrumpMegyn Kelly blames member of Trump transition team for death threats Lewandowski: We can say 'Merry Christmas' again under Trump Trump to visit Ohio State victims MORE.  Cruz was once considered to have the inside track on South Carolina due to its strong contingent of evangelical voters and Rubio’s strong showing will give his campaign new life headed into the Nevada caucuses.

The Huffington Post reported that Romney, who easily won Nevada in 2008 and 2012, could endorse Rubio before the GOP caucuses on Tuesday.

A Rubio adviser, however, questioned the report, tweeting on Sunday morning that it would be a "bizarre" strategy not to tell the senator's campaign and break the news in The Huffington Post.

--This report was updated at 9:10 a.m.