In the World Snooker Championship matches are decided over 25 frames. The first player to win 13 frames is thus the winner, irrespective of whether the other player has won 0 or 12. Imagine, therefore, that, after 22 frames, the score stands at 12-10. Obviously the leading player has a distinct advantage. He need only win one more frame to secure the match. The other player, by contrast, needs to win all the remaining frames.
For some time now - really since the Wisconsin primary - Obama has had those 12 frames. Any one of the heavily contested primaries - Ohio, Texas or Pennsylvania - could have given him victory. Clinton needed to win all three to stay competitive. And she won all three. She has narrowed the gap.
In some ways Obama, while still leading, moves on to the defensive. There is only one remaining contest where a Clinton win is discounted in the market - Puerto Rico. He can deliver a knockout blow there, but nowhere else. Indiana has, for some time, been within the margin of error. Whoever wins there will gain significant momentum, but it will not be an upset.
Obama, however, is struggling with the expectation of victory in both Oregon and Kentucky. In both cases his lead is narrow. If Clinton wins either state it would be a major blow to Obama.
His biggest expectations are in North Carolina. A Clnton victory there could easily produce a rush of super-delegates to her cause. But given that around half the voters are likely to be Black, a Clinton victory is very unlikely. I doubt that the controversy surrounding the Rev. Jeremiah Wright will hurt Obama with Black voters. Clinton would therefore need to do as well with Whites as he does with Blacks - ie win 90% of the vote - to even tie the state. It is possible, though, that his victory could be Pyrrhic. If Clinton narrows the gap to five points the narrative will focus on Obama as the candidate who tried to reach out beyond Jesse Jackson's base, and ultimately failed to gain the confidence of White voters.
There is, however, one additional game being played here, and in this case it is Clinton who has quietly acted below the radar to gain that 12-10 advantage: Florida and Michigan. She won both states by convincing margins. The threat of revotes has been averted. There are three remaining battles: The Rules Committee will consider the matter; In June, jurisdiction passes to the Credentials Committee; and the Convention itself can overturn the decision of either committee.
This three part battle aids Clinton because, if Florida and Michigan are ever admitted, it will be almost impossible to kick them out. If she wins any of these three battles the delegates will be seated, whereas Obama needs to win all three to keep them out.
There is a situation in snooker where you leave your opponent with a near impossible shot. The ball he is trying to aim at is trapped behind other balls, and hitting them incurs a penalty. This is called a snooker. A win for Clinton at either committee snookers Obama. He can aim, without a line of sight connection, to hit his target ball, but he will probably miss. And he will probably incur a penalty - losing Florida and Michigan in the general election - if he even tries.