Bernie Sanders is packing arenas with record crowds, enjoying a formidable lead in New Hampshire, pulling closer to Hillary Clinton in Iowa, and nearly matching Clinton in fundraising, but the former secretary of state retains a decisive advantage in the so-called invisible primary: the process whereby party elites, donors, and interest groups coalesce behind a candidate.

Nowhere is Clinton's advantage within the party establishment clearer than in the lopsided endorsements of Democratic governors and members of Congress. Clinton has secured the backing of 153 such figures, compared with three for potential candidate Vice President Joe Biden, and one for former Maryland Gov. Martin O'Malley.

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Not surprisingly for a self-described democratic socialist who revels in taking on the powers that be, Sanders started the week with a grand total of zero gubernatorial and congressional endorsements.

That's about to change. The Los Angeles Times' Mark Barabak reports that Arizona congressman Raul Grijalva, the co-chairman of the Congressional Progressive Caucus and a frequent critic of the Obama administration from the left, is set to lend his support to Sanders's insurgent bid:

That, however, is about to change, as Arizona Rep. Raul Grijalva prepares to declare his support for Sanders' presidential bid. The announcement is expected Friday night when the two appear together at a Tucson rally, part of a Sanders swing through the West ahead of next week's first Democratic debate, in Las Vegas. Grijalva, a liberal Democrat serving his seventh term representing a southern Arizona district including Tucson, is co-chairman of the Congressional Progressive Caucus, which Sanders -- a self-described Democratic socialist -- helped cofound as a House member in 1991.

The impending endorsement of the long-serving Latino lawmaker comes as Sanders seeks to expand his base of support beyond the white progressives who dominate the Iowa caucuses and New Hampshire primary, but are not representative of the Democratic electorate writ large. A national Public Policy Polling survey released Tuesday offers the Sanders camp a glimmer of hope: While the poll found him continuing to lag among black Democrats, taking 13 percent of their votes to Clinton's 51 percent and Biden's 30 percent, Sanders comes closer among Latinos: Clinton captured 43 percent of their votes to Sanders's 26 percent and Biden's 18 percent.