Hi,
Here is the opening statement of that piece of news:
"Former U.S. president George H.W. Bush has backed front-runner John
McCain in his bid to become the Republican party's presidential
candidate."
Currently, McCain still has to compete against Huckabee. He will become the Republican party's presidential
candidate if he can get 1191 delegates, 1 over 1190, which is the top delegate marker. Therefore, over the top here means getting over that marker - to become the only man from the Republican party to run against either Clinton or Obama, not to become the president of the U.S.
By the way, I might just be me, but I like the phrase "help push / put McCain over the top" better than "help McCain over the top."