"Here is my concern, we can lose in 2016 and we probably will," Graham stated in an interview with MSNBC.
The senator argued that businessman Donald Trump, who is currently leading in popularity among Republicans, will get whipped out in a match-up with Democratic candidate Hillary Clinton. He also described the billionaire as an unreliable conservative Republican.
Graham suggested that Senator Ted Cruz is a more competitive candidate.
"I don’t know if he [Cruz] can beat her [Clinton] or not, but at least we’ve got a fighting chance," he added.
Trump has been widely criticized for his controversial statements, including in relation to immigrants, Muslims, and women.
However, anti-Trump forces among the Republican Party establishment have been suffering setbacks, since Trump is far ahead of all his potential challengers in the popular Republican primary vote nationwide.