Behind the scenes, allies of Jeb Bush and Marco Rubio are bracing for an intense and bruising competition between the two longtime allies, who are vying for the Republican nomination for president. But you'd never know that from reading Rubio's statement welcoming Bush to the race on Monday.

"In politics, people throw around the word 'friend' so much it often has little real meaning," Rubio said in the statement lauding the former Florida governor. "This is not one of those times. When I call Jeb Bush my friend, I mean he is someone I like, care for and respect. He and I have worked closely together for many years, on issues big and small. He is a passionate advocate for what he believes, and I welcome him to the race."

Bush, who is officially kicking off his campaign Monday, mentored Rubio, a Florida senator, as he worked his way up through the Florida political ranks. The two candidates are seen as early front-runners for the Republican nomination and are already racing to secure the support of donors and other supporters in Florida and across the country. The race has divided Republicans in South Florida, the home base of both contenders.

On Twitter, Bush thanked Rubio for his warm welcome: