Democratic presidential candidate Bernie Sanders says he'll remain in the primary race despite calls from rival Hillary Clinton to quit, adding that based on the delegate count, he believes the Democratic party convention will be a contested event. (Reuters)

THE MORNING PLUM:

Bernie Sanders has now threatened perhaps more directly than ever before to take the Dem nominating contest all the way to the floor of the convention in Philadelphia in July, arguing that while this may be a real long shot, he can still win the nomination by flipping super-delegates to his side. If Sanders wins in Indiana tomorrow, he’ll likely renew that threat with even more gusto.

But even if you look at the math precisely the way Sanders is asking us to — and unquestioningly grant him the mathematical concessions he is requesting — he is still all but certain not to win the nomination.

At a press conference late yesterday, Sanders said unpledged delegates — or the “super-delegates” who are free to back the candidate of their choice — in states that he won by landslides should all back him, and said they should back Clinton in states she won:

“It is virtually impossible for Secretary Clinton to win the majority of convention delegates by June 14th with pledged delegates alone. She will need super-delegates to take her over the top at the convention in Philadelphia. In other words, the convention will be a contested contest….those super-delegates in states where either candidate — Secretary Clinton or myself — has won a landslide victory, those super-delegates ought to seriously reflect on whether they should cast their super-delegate vote in line with the wishes of the people of their states.”

But even granting Sanders this concession, the math still doesn’t work for him. Per figures supplied by the DNC, if you give Sanders all of the super-delegates in all of the states he has won so far, the total is around 150. If you give Clinton all of the super-delegates in all the states she won, the total is around 375. If, for good measure, you were to also give Sanders all of the super-delegates in Indiana and in California (both of which Sanders says he has a good chance at winning), Sanders would still be around 100 super-delegates behind Clinton. That would not help Sanders close the gap among pledged delegates, obviously.

To be sure, Sanders also said yesterday that on top of the super-delegates in the states he’s won, he’d also need to win over many other remaining super-delegates, too, which he said he can still do by arguing that he’s the more electable candidate this fall. At his presser, Sanders acknowledged that in order to catch Clinton in pledged delegates, he’d have to win “65 percent” of the remaining ones, which he admitted would be very hard (though he insisted it is “not impossible”). And so, in this scenario, Sanders would be explicitly asking the super-delegates as a bloc to engineer the nomination for the candidate who trails in both the pledged delegate count and the popular vote.

Even some of the liberal groups backing Sanders have said calling on the super-delegates to flip the outcome is a non-starter. And it’s very hard to imagine Sanders seriously continuing with this argument, given that he has been asserting for months that the Dem establishment is rigging the process on Clinton’s behalf. But Sanders theoretically could push this all the way to the convention, by refusing to concede, even after the voting concluded and Clinton still held a lead in all the key metrics.

Josh Putnam, an expert in party rules and political science lecturer at the University of Georgia, says that if Sanders really did this, it would force a formal roll call vote by delegates during the convention proceedings. “It would not go his way,” Putnam tells me. “He might be able to peel a few super-delegates off here and there. But the vast majority would continue to stay with Clinton.”

Putnam adds that in the weeks before the convention, there would be public whip counts on the delegate math that would reveal Clinton to be well ahead among super-delegates as they made their final decisions. “The writing will already be on the wall,” Putnam says.

So the question for Sanders is this. If, after the voting concludes, Clinton leads in the pledged delegate count and the popular vote — and he makes one last pitch to super-delegates, and they refuse to flip in significant numbers — will he still force this battle all the way to the convention floor at that point? This, at a time when the party is hoping to unify behind its nominee as an engaged national audience tunes in? Or, if one last pitch to super-delegates in June comes up short, will he concede at that point, enabling the party to unify heading into the convention?

It’s perfectly legitimate for Sanders to keep this going until all the votes are counted. It’s also perfectly legitimate for Sanders to fight on into June, even if he knows he can’t win, for the sole purpose of trying to leverage his national constituency to influence the party’s agenda in the fall elections and beyond. But forcing this battle on to the convention floor — after it’s become unequivocally clear that so doing will not alter the outcome — seems hard to justify. The pressure on Sanders to defend this course of action — and to explain why it is even at all tenable — will likely mount in the days ahead.

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* SANDERS FACES AN EXTREMELY STEEP CLIMB: The First Read crew spells out how tough his path is, no matter how you measure it:

In pledged delegates, Clinton currently holds a lead of 321 delegates with Washington delegates to still be allocated. Clinton must win 35% of remaining pledged delegates to get a majority in pledged delegates. Sanders must win 65% of remaining pledged delegates to get a majority in pledged delegates….

In overall delegates (pledged + super), Clinton holds an overall lead of 790 delegates….Clinton must win 19% of remaining delegates to reach the 2,383 magic number. Sanders must win 81% of remaining delegates to reach the 2,383 magic number.

And the supers just aren’t going to switch en masse. Even doing the math Sanders’s way doesn’t close the gap.

* TRUMP CRUISING IN INDIANA: A new NBC/WSJ/Marist poll finds Donald Trump leading Ted Cruz and John Kasich among likely GOP primary voters in Indiana by 49-34-13. NBC’s Mark Murray comments:

If that margin in Indiana holds on Tuesday, Trump would be on a glide path towards obtaining the 1,237 delegates he needs to win the Republican nomination on a first ballot at the GOP convention in July…58 percent of likely Republican primary voters in Indiana say they disapprove of Cruz and Kasich teaming up to beat Trump in the Hoosier State, while 34 percent say they approve of the move.

The collaboration strategy appears to be backfiring, potentially making Trump have an easier time winning the nomination. The polling averages have it a bit tighter, with Trump up seven.

* TIGHT RACE ON DEM SIDE IN INDIANA: The new NBC/WSJ poll finds Hillary Clinton leading Bernie Sanders among likely Dem primary voters in Indiana by 50-46. As Marist’s polling director puts it:

“Clinton and Sanders are more likely to divide the delegate pool, which will do little to change the narrative on the Democratic side.”

The polling averages have Clinton up a bit more, by 51-44, but whatever happens, the state of the race won’t change much at all.

* CRUZ’S LAST, DESPERATE STAND IN INDIANA: The Post reports that Cruz’s volunteers in Indiana are picking up signs that Trump may be running away with it:

Volunteers said they were hearing misgivings from voters — many rooted in insults that front-runner Donald Trump had hurled at Cruz. Most people who express reservations, explained Megan Kerr, 17, of Fishers, Ind., “are concerned with the nickname he’s been given — ‘Lyin’ Ted.’ ” Frank Cerrone, 68, of Perry Township, Ind., also said “there is some idea that Ted Cruz is rigging the system,” another Trump attack.

It appears GOP voters are inclined to believe Trump when he says the GOP establishment is treating him unfairly.

* GOP EFFORTS TO FIGHT ‘VOTER FRAUD’ ARE WORKING: The New York Times has a good overview of all the voter ID laws that are going into effect this year, and how this could impact the outcome of the fall elections:

As the general election nears — in which new or strengthened voter ID laws will be in place in Texas and 14 other states for the first time in a presidential election — recent academic research indicates that the requirements restrict turnout and disproportionately affect voting by minorities….Most of the strict photo ID laws have been enacted in the past decade by Republican-dominated legislatures.

Many of these were passed in southern states that would have required pre-clearance under the Voting Rights Act until the Supreme Court gutted it, and their goal of restricting voting access in the name of combating voter fraud may have exactly their intended effect.

* TRUMP’S LATEST LIE ABOUT IMMIGRANTS, DEBUNKED: In his big foreign policy speech, Trump claimed that “scores” of recent migrants have been “charged with terrorism,” and that there are “dozens and dozens more” such cases that aren’t even known to the public. Post fact checker Michelle Lee investigates and cannot figure out what source Trump even used for this claim, which turns out to be completely baseless.

This is of a piece with Trump’s frequent tendency to make outlandish claims and justify them by asserting they are based on secret sources that he will not reveal. If his supporters believe him, are the claims really false?

* IN TRUMP, REPUBLICANS REAP WHAT THEY SOWED: E.J. Dionne offers an interesting explanation as to why Republicans are partly to blame for the rise of Trump:

One reason is the anger in a large segment of the Republican Party that has been stoked by its leaders….There is also the utter contempt toward government that their ideology encouraged….phony celebrity populism plays well on television at a time when politics and governing are regularly trashed by those who claim both as their calling. Politicians who don’t want to play their assigned roles make it easy for a role-player to look like the real thing and for a billionaire who flies around on his own plane to look like a populist.

This would perhaps be amusing if the effect of it weren’t also that President Trump is an actual possibility.