The Daily Caller is confirming and has more:

According to sources familiar with the campaign’s thinking, presumptive Republican presidential nominee Mitt Romney is set to endorse Rep. Connie Mack in the Florida Republican primary against George LeMieux.

LeMieux was Charlie Crist’s former Chief of Staff — and the man Crist appointed to the U.S. Senate in 2009. LeMieux described himself then as a “Charlie Crist Republican,” and led an assault on Rubio during the 2009 campaign, but is now trying to remake himself as a tea party candidate.

(It’s also worth noting that Romney endorsed Marco Rubio over Crist two years ago.)

Mack has emerged as the conservative favorite, having been endorsed by Sen. Rand Paul, Rep. Michelle Bachman and the American Conservative Union.

The Florida race is a highly contested one and it looks like Romney is on the side of the TEA Party here. Grassroots power, baby.!/mckaycoppins/status/202802603623596032!/bdomenech/status/202803644792451074!/FixAaron/status/202803585006845955