The main thing to know about superdelegates is that Republicans don’t have them—which they’re regretting as the Trump train comes crashing down the tracks.

The Democratic Party created its firewall of “ex-officio delegates” as a hedge against the kind of electoral disaster the party suffered in 1972 when candidate George McGovern lost in a landslide.

McGovern had won the nomination in a grassroots uprising energized by opposition to the Vietnam War and social movements for civil rights and women’s rights. Republicans dubbed him the candidate of amnesty, abortion, and acid. At the Democratic Convention in Miami, divisions in the party were highlighted when McGovern ousted Chicago Mayor Richard Daley, once the consummate powerbroker, seating instead an Illinois delegation headed by the Rev. Jesse Jackson.

In the wake of McGovern’s historic defeat, the Democratic Party bigwigs shunned in Miami looked for a way to regain some of their lost influence. Three blue-ribbon commissions followed before a compromise was struck between liberal reformers, who wanted zero party officials as delegates, and state chairs and party officials who wanted 25 percent representation.

Democratic Party activist Mark Siegel was part of the ABM effort (Anybody But McGovern), and served on all three commissions. He wrote the rule that emerged calling for 10 percent of the delegates to be party officials—governors, mayors, members of Congress and distinguished party leaders like former presidential candidates and former national party chairs. The Democratic National Committee then added its members, some 300 additional people, boosting the percentage of these uncommitted superdelegates to 15 percent of the total delegates.

“Supers are a hedge against disaster,” Siegel told the Daily Beast. “These are people who by virtue of the office they hold should be included. They’re legitimate… It gives the party some wiggle room to avoid electoral catastrophe.”

In the current cycle, there are 715 supers out of 4,765 total delegates. Of the supers, 473 are pledged to Hillary Clinton, 32 to Bernie Sanders, and 1 to Martin O’Malley, who left the race after Iowa. The rest, 209, are uncommitted.

Ideally, the superdelegates affirm the will of the people, moving in large numbers toward the candidate who receives the most votes in the party’s primaries and caucuses. That’s the argument that Tad Devine, now working for Sanders, made in a 2008 op-ed recalling how worried he was as Walter Mondale’s delegate counter in 1984 when he realized the morning after the last primaries that they were 40 delegates short of a majority. After a frantic round of phone calls, the supers put Mondale over the top by noon.

Devine made the point in his article that this mass of uncommitted convention voters “should resist the impulse and pressure to decide the nomination before the voters have had their say.”

It has been a major irritant to the Sanders campaign that hundreds of supers are pledged to Clinton, some in states where Sanders won more votes. But after attacking superdelegates as elitist establishmentarians who thwart the will of the people, Sanders is now aggressively lobbying many of them for their support.

That’s because the only way he can possibly overtake Clinton in the delegate math is to get backing from the supers. It’s a conundrum Clinton knows well. She lagged behind Barack Obama in delegates in ’08, but she was ahead of him in the popular vote and thought the supers would move to her as the more electable candidate. Instead, they came down on the side of Obama, prioritizing his greater share of earned delegates as representing the will of the people.

Sanders is more than 2 million votes behind Clinton, so it’s hard to see on what basis he would persuade a significant number of superdelegates to endorse him. They tend to be party regulars and Sanders—until last year an independent who caucused with the Democrats, and who’s outright said he’s running as one for the “media exposure”—underscored his lack of allegiance to the Democratic Party when he called a pricey fundraiser hosted by George Clooney “obscene.” The money raised will be pooled among several Democratic Party organizations working to elect Democrats down the ticket.

Asked by MSNBC’s Rachel Maddow if he might direct some of his prodigious fundraising efforts to party building, Sanders offered a noncommittal, “we’ll see,” saying his priority is winning the nomination.

And with his organization now trying to move ex-officio delegates into his column, or at least out of Clinton’s, “he’s moved from railing against ‘superdelegates are terrible, they thwart the will of the people,’ to saying if she’s leading, he’ll still try to win them over,” says Norm Ornstein, a political scientist with the American Enterprise Institute, a conservative think tank.

“For a guy who presumably is in the race because of his moral stance on important issues, he’s looking like a completely selfish, manipulative politician.”

On the Republican side, party elders—with a much smaller cushion of uncommitted delegates, less than 10 percent—are wishing for more successful selfish and manipulative politicians to stop Trump, who needs 54 percent of the remaining delegates to win a majority, from outright claiming the nomination.

“Their nightmare scenario is if he falls 30 or 50 delegates short, and they conspire to deny him the nomination,” says Ornstein.

There are three from each state and territory (national committeeman, national committeewoman, and state chair), plus 112 national committee members. Republicans believe in federalism, so each state is allowed to design within broad parameters how to select its delegates.

And while all Democratic delegates are subject to Candidate Right of Approval, or CRA, the Republicans have that in only 12 states, meaning there are faithless delegates likely to vote with the Stop Trump forces on the convention floor.

These arcane rules only become relevant under extraordinary circumstances like we’re seeing on the Republican side. It’s not unlike the Bush v. Gore recount of 2000, when state laws and provisions that had been on the books for years suddenly became relevant. The system is stressed, and there’s no good outcome other than to let the process play itself out, warts and all.

And that is a recipe for chaos in Cleveland if Trump can’t close the deal before then.

“They”—meaning GOP leadership—“lose either way,” says Siegel. “It’s wholesale robbery or they go over the cliff with a candidate that may even cost them the House.”