The Fix's Philip Bump explains why a contested convention still might not be a realistic path forward for Bernie Sanders. (Peter Stevenson/The Washington Post)

With the Democratic presidential nomination system working the way it does, there are essentially two possible outcomes: A candidate will either win in a blowout, or he or she will need superdelegate votes to gain a majority.

The reason for this is simple: Fifteen percent of all of the Democratic delegates are unbound superdelegates. So unless you have about an 18 percentage-point lead among delegates by the time the voting wraps up, you'll need some superdelegates to put you over the top. This makes the difference between a close race and a blowout a little murky — which can be advantageous to the underdog.

Right now, Hillary Clinton has about a 10 percentage-point delegate lead over Bernie Sanders. (For comparison: Barack Obama's pledged delegate lead was only about four percentage points by the end of the 2008 race.) The current margin is not likely to change much between now and the end of the contest, with the two likely to play to a draw in California, Clinton to win big in New Jersey and D.C., and Sanders to triumph in smaller states between now and the end of the race. For it to change significantly in Sanders's favor, he'd need to do very, very well in California and New Jersey in particular, a promise that he has issued often and delivered rarely.

One of the things that Sanders has been very good at, though, is conveying a convincing depiction of a guy who's going to come from behind and win this thing, even as he has continued to trail badly or dropped further behind. During a news conference in Washington on Sunday marking the first anniversary of his campaign launch, Sanders insisted that the math above means that the Democrats were headed to a "contested convention," leveraging the now-common language of the ferocious (and unsettled) Republican contest to paint his own contest as similarly unsettled.

"It is virtually impossible for Secretary Clinton to reach the majority of convention delegates by June 14 with pledged delegates alone," he said. "She will need superdelegates to take her over the top at the convention in Philadelphia. In other words, the convention will be a contested contest."

That's true — mostly because, unlike in 2008, Sanders will contest it. Eight years ago, Clinton conceded the race before the convention, recognizing that trying to fight her way to victory on the convention floor was likely to fail, despite her having a slight lead in the popular vote. But Clinton realized the damage that could be done to the party — and perhaps herself — so she didn't.

Sanders doesn't share the former sentiment, as he has made clear. He was an independent until he decided to run for president, and his goal during his campaign has been to upend the system, into which a convention floor fight fits neatly.

But that doesn't mean he has any real shot at winning.

Sanders, like Clinton, needs superdelegates to win. Even if it were he who led by 10 percentage-points among pledged delegates, he'd need them. So let's consider his arguments for why they should give him their votes.

The "momentum" argument

Back in the halcyon days of Sanders's "momentum," when he'd won seven of eight contests in a row, including a big win in Washington, his argument was that the momentum would propel him through the end of the voting in June, offering a compelling argument to superdelegates that the will of the party now rested with him, and that Clinton's early support was therefore negated. Then he lost five of the last six races — and Clinton's delegate lead returned to about what it was in the middle of March. The momentum was, as many had suspected, a function of several Sanders-favorable races clustered in a short window (as was the recent streak by Clinton). The race hadn't really changed at all.

Now, it seems, Sanders's argument will be that his strong performances at the tail end of the contest, including a win in California — coupled with close national polling — should provide the same motivation to superdelegates to embrace his candidacy. Sanders is who the party now wants to win.

There are a few flaws in that argument, including that Sanders's one-point deficit in the national Real Clear Politics polling average — which came right after those seven wins — has now widened to four points. The biggest problem for Sanders, though, is that, unlike on the Republican side, California isn't the last contest. The last contest for the Democrats is the D.C. primary, on June 14. And there is essentially no way that Clinton will lose that contest, given how strongly she has performed in places with large black populations.

Meaning that the last voting will almost certainly reinforce Clinton's dominance — while reminding superdelegates why Clinton has such a big lead: black voters. It is black voters who helped Clinton run up huge wins in New York and Maryland last week, on March 15 and in southern states before that. D.C. will almost certainly make that point once again, with emphasis.

The pledged delegate argument

On CBS on Sunday, Sanders insisted that his campaign might still win the majority of pledged delegates. "We need to win 65 percent of those votes," he said of the remaining total. "The states coming up are favorable to us."


The problem for Sanders is, as it has always been, that Democratic contests are all proportional. He needs to win every state by a wide margin to hit his goal. The other problem for him is that nearly half of the remaining delegates are in California. If he and Clinton essentially tie there — or even if he wins by five points, which polling suggests won't happen — he needs three-quarters of the delegates everywhere else to make up for it (including New Jersey and D.C.).

Could he win pledged delegates? Yes, in the sense that he could win the lottery.

Superdelegates should vote the way their states did

During the news conference, Sanders suggested that superdelegates had an obligation to reflect the will of the voters in their states.

"Those superdelegates in states where either Secretary Clinton or myself has won a landslide victory — those superdelegates ought to seriously reflect on whether they should cast their superdelegate vote in line with the wishes of the people of their states," he said. He notes Washington in particular, a state with 17 superdelegates and a state he won by a large margin.

We looked at this a few weeks ago. Mandating that superdelegates in a state back the candidate who won narrows Clinton's lead, but doesn't erase it. If you mandate that the superdelegates be divvied up proportionally, the margin for Clinton narrows further. But, in the same way that she still has a lead in pledged delegates because of proportional distribution, she has a lead with superdelegates, too.

So none of those arguments is terribly strong. But even if they were more solid, there's a simple rebuttal to Sanders for which he has offered no real response: He's trailing in actual votes by an insurmountable margin.

Before Clinton's big wins in New York and the Northeast, our fact-checkers pegged her actual vote lead at 2.4 million. She got nearly 300,000 more votes in New York, 250,000 in Maryland and 200,000 in Pennsylvania. Sanders won Rhode Island, clawing back 14,000 votes. But Clinton now has well over 3 million more votes than Sanders.

What Sanders is asking superdelegates to do is ignore that lead. His supporters have a surfeit of unsubstantiated explanations for this gap (such as voter fraud), but it's not complicated. Clinton leads because more people voted for her. In 2008, Obama led because of strategic delegate accumulation; that's not why Clinton leads now.

Sanders asks that superdelegates set aside that the choices of those voters — many or most of them black — because he did well in Washington and maybe is close in national polling. It's impossible to see whom that will convince.

It's true that Sanders and Clinton are headed to a contested convention, if Sanders wants it. That doesn't mean, as it would on the Republican side, that the outcome is up in the air. Sanders's campaign slashed its staff as it announced that, for the first time this year, it didn't crush Clinton in fundraising. For there to be a contested convention, Sanders would need to convince his base that he can win one — and therefore to keep funding his efforts through California. He's welcome to do that; they're welcome to keep giving.

But what's going to happen at that convention is not much of a mystery.