Report: Romney to endorse Rubio

Former GOP presidential nominee Mitt Romney will endorse Marco RubioMarco RubioMexican politicians have a new piñata: Donald Trump Bush ethics lawyer: Congress must tell Trump not to fire Mueller The private alternative to the National Flood Insurance Program  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 TrumpMellman: Trump love? Overnight Cybersecurity: Senate Judiciary reportedly drops Manafort subpoena | Kushner meets with House Intel | House passes Russia sanctions deal | What to watch at 'hacker summer camp' Don’t cut Public Service Loan Forgiveness program 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.