"Today I believe that I am being called to lead by helping to clear the field in this race so that a positive, conservative message can rise to the top of the field.
"With this in mind, I will suspend my campaign immediately. I would encourage other Republican presidential candidates to do the same, so that the voters can focus on a limited number of candidates who can offer a positive, conservative alternative to the current frontrunner.
"Sadly, the debate taking place in the Republican party today is not focused on that optimistic view of America. Instead, it has drifted into personal attacks," Walker said.