I found the phrase “*his to lose*” in today’s Associate Press news reporting Herman Cain’s sexual harassment allegation under the lengthy caption “Cain seeks to put aside harassment allegations even as lawyer for accuser presses on.” 

It appears in the following lines:

“Romney is running his second national campaign and has spent the past few weeks shoring up support among the GOP establishment for *a nomination fight many Republican insiders think is his to lose.”*

I first thought “his to lose” means he will certainly to lose, which sounds very odd to say at this stage. So I checked the exact meaning of the phrase on online dictionaries, and got the quite contrary definition on wiki.answers.com, that says: 

"It means that someone is winning by so much, that the only way he could lose at that point would be if he defeated himself, i.e. by 'choking' or 'dropping the ball.'"

I’m interested in how did “his to lose” come to mean he is sure to win (the game / fight) unless he should blunder (defeat himself) in quite reversal way from its surfacial look – his to lose? 

Although I see growing increase of the incidence of the usage of this phrase since 1980 after the first peak in early 1900 in Google Ngram, Is this a very popular phrase among English speaking society today?