Sen. Hillary Clinton is trailing Sen. Barack Obama and has almost no shot of getting the Democratic nomination. Some have been calling for her to step down, fearing the collateral damage of a long nomination battle.

But with just three primaries to go, Clinton has her sights set on Puerto Rico as she hopes to post a popular vote victory - depending on how you tally that math, of course - and make her case for the nomination.

Clinton trails Obama in delegates, 1,974-1,780, with 2,026 needed to win. Puerto Rico, which holds its primary Sunday, June 1, has 55 delegates at stake. South Dakota (15 delegates) and Montana (16) vote June 3.

Obama has amassed 16,685,941 (49.1 percent) total votes to Clinton’s 16,227,514 (47.7) - without barred contests in Florida and Michigan.

Adding Florida’s votes cuts his lead from 458,427 to 163,655. Michigan and Florida combined give HRC the edge - though it’s almost impossible to see Michigan counted by the DNC, as Barack Obama wasn’t even on the ballot.

With an expected win in Puerto Rico and losses in South Dakota and Montana, what can Hillary Clinton hope for as the primaries end?

Puerto Rico has about 4 million people, slightly more than Oregon and Kentucky, which voted last week. A landslide 36 percent win in Kentucky on May 20 netted Hillary Clinton nearly 250,000 votes.

That’s a lot to hope for again, but a similar result in P.R. would likely give her the popular vote lead if Florida votes are included. Without her questionable inclusion of the Sunshine State, this popular vote race is game over - and since it’s delegates that decide this anyway, the point is likely altogether moot.

As for the remaining 86 pledged delegates, if Obama and Clinton split them evenly, he’ll be on the cusp of the 2,026 needed to clinch the Democratic nomination. If Obama loses Puerto Rico 60-40 percent, but wins South Dakota and Montana by more than that, this scenario would be about right.

[SIDE NOTE: since it's not even a state and can't vote in the general election, does anyone else find it ironic that Hillary Clinton - who would easily dismiss the June 1 contest as meaningless if Barack Obama were favored to win - is now campaigning in Puerto Rico so vigorously?]

An April poll put Clinton up 50-37 percent in Puerto Rico, but that margin is likely to widen, making 60-40 seem reasonable. Obama has dominated Western states so far, so a split (more or less) of the 86 pledged delegates left on the table seems fairly likely if past results are any indication.

If and when that happens, only a handful of undecided or defecting superdelegates would be needed to officially put Barack Obama over the threshold.

Until then, he can expect the Clinton campaign to continue running, clinging to whatever hope, flimsy math or conspiracy theories it can muster.