Where From Here

Realistically, Sanders has peaked.  If Hillary hold on to her 20 point lead in South Carolina - polling averages have her +24 - she will begin to dent Sanders energy.  On March 1st, she can be reasonably expected to win Texas, Georgia, Virginia, Minnesota, Tennessee, Alabama, Arkansas and Oklahoma.  That would leave Sanders with Vermont and probably Massachusetts.  Sanders will stick around, but the momentum will be clear.  Unlike in 2008, when Obama traded states with Clinton and racked up delegates, Sanders doesn't have a ton of states where he can be expected to put a dent into her delegate lead.  He will keep campaigning, because he wants to keep his issue agenda alive.  But he's probably done.

Once again, the GOP is more interesting.

Who benefits from Bush's departure?  The obvious candidates are Rubio and Kasich.  But Bush's support was so flaccid, that if his voters split between the two establishment candidates - I'm not calling Rubio a moderate - it is unlikely to let one guy break clear.  Carson - because his campaign has always been an elaborate grift -  continues to run so that he can build his email list and employ family members and hangers on.

So we are left with the Four Horsemen of the Apocalypse.  State by state polling is sketchy, so there are rough estimations.

Trump: Georgia, Alabama, Massachusetts and Alaska seem safe bets.  Tennessee and maybe Oklahoma, too.

Cruz: Texas, Arkansas and maybe Oklahoma.

Rubio: Virginia and Minnesota, though I could see Kasich stealing his thunder there.

If Trump continues to win - even by small margins - he's the nominee.  Cruz and Rubio have to start winning states.

Here are the delegate counts, so you'll see what I mean:

GOP (1,237 needed to win)
Trump - 61
Cruz - 11
Rubio - 10
Kasich - 5
Bush - 4
Carson - 3

If Trump keeps accumulating delegates at those ratios, he's going to pull ahead in March to a place where the Establishment can't catch him.

On the Democratic side (2,382 needed to win)

Clinton - 51
Sanders - 51

However, when you add in the Super delegates:

Clinton - 500
Sanders - 70

That's the math.  Sanders has to start winning to overcome party resistance - and winning is not in his future.  Someone has to start edging into Trump's delegate lead - and no one seems to be doing that.

March 15th in the critical day for the GOP.  Florida, Illinois, Missouri and Ohio are all winner-take-all primaries, and Florida and Ohio have favorite-son candidates.  If the GOP can't stop Trump there, they can't stop him.