President Obama is endorsing Sen. Brian SchatzBrian Emanuel SchatzDem senator: 'This is not my president' Trump defiant: 'Blame on both sides' in Charlottesville Dem senator: CBO confirms ObamaCare repeal is a '%#$@ sandwich' MORE (D-Hawaii), giving him a potentially big boost in his Democratic primary.

"Brian's deep commitment to the people of Hawaii and his effective leadership are why I believe it is important to return him to the Senate," Obama said in a statement released by Schatz's campaign. "Senator Schatz is protecting Hawaii's values and fighting every day on behalf of middle-class families.  There is no question that Senator Schatz is the right choice to continue delivering for Hawaii."

Schatz, who was appointed to the Senate in late 2012, is facing a tough primary challenge from Rep. Colleen Hanabusa (D-Hawaii). Public polling has shown the primary is a dead heat. 

He has deep ties to Obama — Schatz chaired Obama's 2008 presidential campaign in Hawaii, and some of his staff are former Obama aides. 

Obama's endorsement could be a major development for Schatz in the race. The president remains very popular in his home state, where he won 71 percent of the vote in 2012.