The Honolulu mayor’s race may be officially nonpartisan, but U.S. Sen. Brian Schatz says he is endorsing Honolulu Mayor Kirk Caldwell in large part because of their shared roots in the Democratic Party.

Schatz announced his endorsement decision in an interview last week, saying the city “is at a critical juncture in terms of the kind of leadership that we need.”

“I think this year more than ever it’s important that we elect Democrats because values do matter in your perspective on government and its relationship to the people it serves,” Schatz said. “It matters very much, and Kirk shares my values.”

In the islandwide primary election on Aug. 13, Caldwell received 44.6 percent of the votes cast, while Republican former City Councilman and U.S. Rep. Charles Djou captured 43.7 percent. The two candidates now advance to a runoff election in November.

Heading into the November contest, the Caldwell campaign apparently hopes to capitalize on the strong Democratic leanings of many Oahu voters to try to garner support for Caldwell, and to persuade voters to reject Djou for his party affiliation.

However, Djou has won endorsements from prominent Democrats such as former Gov. Ben Cayetano and Honolulu City Councilwoman Ann Kobayashi, and former Democratic Party Chairman Walter Heen is serving as Djou’s campaign chairman.

Schatz contends Caldwell is the only candidate with a “realistic plan” to complete the $8.1 billion Honolulu rail line from East Kapolei to Ala Moana Center. That project is now far over budget, and faces a funding shortfall that may be as large as $1.5 billion.