Democracy for America, the liberal group founded by former Vermont Gov. Howard Dean (D), is endorsing Sen. Brian SchatzBrian Emanuel SchatzOvernight Tech: AT&T chief takes the stand to defend merger | Facebook keeps most users out of EU data law's reach | HUD reopens probe into Facebook housing ads | Venture capital firms go to bat for cryptocurrencies Facebook investigated over alleged housing discrimination Senate confirms Trump’s pick to lead NASA MORE (D-Hawaii) in his primary against Rep. Colleen HanabusaColleen Wakako HanabusaFormer Sen. Daniel Akaka of Hawaii dies at 93 Zinke defends use of Japanese word: How could saying good morning 'be bad'? With bills on the table, Congress must heed the call to fix our national parks MORE (D-Hawaii).

Schatz is the first Senate candidate the organization has endorsed this election cycle — and the second incumbent, as they're also backing Rep. Mike Honda (D-Calif.) in his primary against Democrat Ro Khanna.

Democracy for America is latest national liberal group to back him in the race, which could help Schatz keep his big fundraising edge against his challenger and shore up his claim that he's the more liberal candidate in the race.

"Senator Brian Schatz isn't just a reliable vote for progressives in Washington, D.C., he takes it a step further and organizes other Senators to join him. Whether it's fighting on the front lines against climate change, defending a woman's right to choose, or expanding Social Security, Brian Schatz has proven he's a true progressive leader," Democracy for America Executive Director Charles Chamberlain says in an email that will be sent to supporters on Tuesday.

The organization, which was founded by Dean and is run by his brother, Jim Dean, is the latest national liberal group to back Schatz. He also has support from, the Sierra Club, the League of Conservation Voters and the Democratic Senatorial Campaign Committee.

Schatz was appointed to the Senate after Sen. Daniel Inouye (D-Hawaii) died in late 2012, despite Inouye's deathbed wish that Hanabusa replace him. She soon decided to challenge him for the seat. Inouye's widow is backing Hanabusa in the race, as are former Sen. Dan Akaka (D-Hawaii) and former Hawaii governors George Ariyoshi (D) and Ben Cayetano (D).

Schatz, with the help of national groups, has been aiming to make the race an ideological one about who is the more liberal candidate. Hanabusa, who is of Japanese descent, is counting on the state's ethnic mix playing in her favor for the August primary. Asian-Americans and native Hawaiians play a major part in Democratic primaries in the state.

Schatz has led Hanabusa by wide margins in fundraising. He had $2.4 million in the bank as of the end of 2013, while she has less than $900,000. There has been little public polling of the race, but Hanabusa led a Honolulu Star-Advertiser poll released earlier this month, 48 percent to 40 percent.