Rubio has also been often mentioned as a possible VP pick on a GOP ticket, no matter who the nominee is. The Floridian's meteoric rise through the GOP ranks was fueled by his victory over moderate Charlie Crist in the 2010 election. Romney rival Gingrich had actually attacked Romney as being similar to Crist as a Republican moderate.
Rubio has said that Romney "was one of the first national Republican leaders to endorse me. He came to Florida, campaigned hard for me and made a real difference in my race." His endorsement isn't much of a surprise, but could lend to the inevitability narrative building up around Mitt Romney.
Ex-governor Jeb Bush is a previous high-profile Florida Republican to previously endorse Romney.