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Bill de Blasio the latest progressive not to endorse Bernie Sanders

The New York City mayor is the latest progressive leader to line up for Clinton — leaving few remaining major endorsements for Sanders.

New York City Mayor Bill de Blasio's endorsement of Hillary Clinton Friday puts yet another major progressive leader in her column, and out of reach of Sen. Bernie Sanders, her main rival for the Democratic nomination.

De Blasio’s endorsement is no surprise — he worked for and is close with both Clintons and even managed her 2000 Senate campaign. But it comes after a very public delay in which he said he would evaluate each candidate in the race to see which would best exemplify his progressive ideals. 

A new NBC News online SurveyMonkey poll, taken after Vice President Joe Biden said he would not enter the 2016 race, shows Clinton with a 20 point lead ahead of Sanders. 

RELATED: Bernie Sanders calls aide’s comments on Clinton ‘inappropriate’

By the time de Blasio finally endorsed Clinton on MSNBC’s “Morning Joe” Friday, the nod from a national liberal leader had become so de rigueur that Clinton’s campaign barely touted the news, burying his endorsement in a list of a 135 mayors supporting Clinton. 

That’s because he's just the latest progressive favorite to pick Clinton over Sanders.

Earlier this week, she secured the endorsement of Ohio Sen. Sherrod Brown, a close ally of Sanders in the Senate. His support was all the more notable because he stayed neutral in the 2008 Democratic primary and could have done so again for 2016.

Clinton has the support of 35 out of 44 Democrats in the Senate, and at least 121 of the 188 Democrats in the House, not to mention 10 out of 18 Democratic governors, according to FiveThirtyEight's endorsement tracker. Sanders has just two House members in his camp. 

Asked about Brown’s endorsement earlier this week, Sanders dismissed the nod as “establishment support.”

“Oh, I think Secretary Clinton will have almost all of the establishment support,” the candidate told North Dakota NBC affiliate KVLY. “We’re not going to win the establishment. We’re not going to win a whole lot of senators or a whole lot of members of the House. But what we will win, I think, are the American people, working people, young people, senior citizens.”

Many have compared Sanders’ campaign to the 2004 presidential bid of his fellow Vermonter Howard Dean, who enjoyed a wave of popular support that crested too soon and subsided before voters went to the polls in Iowa and New Hampshire.

But even Dean earned major endorsements, notably from Al Gore in December, the former vice president and the party’s immediate prior presidential nominee. He also earned the support of former Sen. Bill Bradley, Gore’s top rival for the 2000 nomination, and longtime Iowa Sen. Tom Harkin. On the very same day in early November, Dean earned the support of AFSCME and SEIU, two of the largest and most powerful unions in the country.

Sanders could still pick up major endorsements, and there are handful of big prizes left to be claimed. The senator met with Biden for an hour Thursday. Sen. Elizabeth Warren has yet to publicly declare support, and the labor union SEIU also has not offered an endorsement.

But Clinton adds to her pile of supporters every day, and the backing of people like Sherrod Brown and Bill de Blasio — not to mention Howard Dean — have led some Democrats to assume even the progressive wing of the party is starting to coalesce around Clinton. 

That may not be a problem if Sanders is correct that people power beats establishment support. But history says otherwise and it may take nothing less than the political revolution he’s calling for in order to win the election.