John Glenn was only the 5th man in space , Yuri Gagarin of the USSR was the first . Glenn was not even the first USA space man , Alan Sheppard had that distinction. Sheppard was just shot into space on a suborbital 'hop'.
The USA was so far behind the USSR that a sub orbital hop was all they could do. Glenn was the first USA manned orbital flight
Gagarin's fully orbital flight put the fear of Armageddon into the USA , it meant that the USSR could launch an orbital nuclear bomb which could then be programmed to re-enter the atmosphere to drop on the USA. Such an orbital bomb would have been undetectable until it exploded , the significance was that the USSR could have wiped out the USA at will if it so desired. The USA realised that it's ' X' series rocket aircraft technology was fundamentally flawed and hastily strapped Sheppard on to the top of a converted missile and sent him on his 'hop'.