Progressives are plotting a weekend push to end the superdelegate system that helped Hillary Clinton clinch the Democratic nomination, at a meeting that will put together the rules for next week's Democratic convention.

Sen. Bernie Sanders roused his legions of fans by blasting the party's use of superdelegates, which are free to vote for any candidate on the convention floor regardless of the results of their state's primary contest. While the effort will come too late to spare Sanders from defeat, his supporters are determined to alter the system they hold responsible for Clinton's victory.

A petition asking voters to pledge their support to "end superdelegates" had garnered nearly 140,000 signatures after the final day of the Republican convention.

"We urge members of the Rules Committee to introduce, demand a vote on, and support language" that binds all delegates to the results of "popular primary and/or caucus processes," the petition said.

Brad Bannon, a Democratic strategist, said the results of the anti-superdelegate movement might not be instant. "When in doubt, create a commission," Bannon said.

"I think the platform committee is going to call for the creation of a blue-ribbon commission to study party rules that will include superdelegates. It will include broadening Democratic primary voters," he added. "I don't think the platform committee is going to do anything to immediately change the status quo."

It was a commission, Bannon noted, that yielded the superdelegate system in the first place.

After Jimmy Carter's landslide loss to Ronald Reagan in 1980, a Democratic Party commission decided to apportion a certain percentage of delegates each cycle to remain unpledged until the convention. In 1984, the first election in which superdelegates were used, Walter Mondale won the party's nomination in part because of the support of the new, unpledged delegates.

Supporters of Sanders' campaign expressed outrage after the New Hampshire primary in February, when the Vermont senator bested Clinton by a more than 20-point margin but tied her in delegates because the state's superdelegates swung in favor of the former secretary of state.

In the series of contests that followed, Sanders argued that the media's failure to distinguish between pledged delegates and superdelegates when reporting where each candidate stood gave voters a false sense of the race. He claimed it was much closer than the delegate counts suggested.

Mark Alderman, a Democratic strategist and former member of the Obama-Biden transition team, said he does not expect Sanders supporters to bring up the issue after convention proceedings begin.

"I doubt that anything goes to the convention floor," Alderman said. "I doubt seriously that you will see anything like what you saw in Cleveland."

Alderman was referring to a last-minute scramble by a handful of state delegations at the GOP convention to force a roll call vote on the rules hammered out earlier in a meeting of the Republican Party's rules committee, a move that would have embarrassed Donald Trump's campaign had it been successful.

"It will all get worked out where it belongs, which is at the committee level," Alderman said.

"I think the Sanders supporters are with the program," he added. "I think that they have some issues they care deeply about, and I am sure they are going to push for those at the rules committee."

More than 50 members of the DNC rules committee are reportedly planning to put forward proposals that would strip superdelegates of their power in the primary. The group includes supporters of both Sanders and Clinton and is being promoted by progressive groups such as MoveOn and Democracy for America.

Alderman said the display of disunity that marked the first day of the Republican convention likely inspired the DNC to "redouble" its efforts to ensure Sanders supporters and Clinton supporters "act like one big, happy family" when they reach Philadelphia.