Democratic presidential candidate Bernie Sanders has enjoyed massive support from voters around the US, but until now he has fallen behind fellow Democrat Hillary Clinton in the quest for congressional endorsements. Sanders is expected to receive his first congressional endorsement from Arizona Congressman Raul Grijalva.

The endorsement is expected to be announced on 9 October when the two join forces for Sanders' Tucson rally, just days before the first Democratic debate in Las Vegas, Nevada. According to the Los Angeles Times, Grijalva is a liberal Democrat who is the co-chairman of the Congressional Progressive Caucus, which Sanders co-founded as a House member in 1991.

Grijalva, also a member of the Congressional Hispanic Caucus, is also expected to help Sanders reach out to Latino voters. Earlier this month, Sanders's campaign announced the Vermont senator had named his Latino outreach director. Arturo Carmona will not only be in charge of reaching out to Latinos, he will also direct Sanders's southwest campaign.

The Huffington Post noted that congressional endorsement help predict who will win the party's primary. Sanders's biggest opponent, party front-runner Hillary Clinton, has managed to grab over 100 endorsements from members of the House and Senate. Meanwhile, fellow Democratic candidate Martin O'Malley also has one congressional endorsement: California Representative Eric Swalwell.

In Sanders' home state of Vermont, Governor Peter Shumlin and Senator Patrick Leahy have both endorsed Clinton. The latest election poll by Public Policy Polling revealed Sanders continues to trail Clinton among Democratic voters, 42% to 24%. Sanders is followed by Vice President Joe Biden, who has not entered the race, with 20%.