Clinton quickly concedes defeat in NH primary

Presidential contender Hillary ClintonHillary Diane Rodham ClintonIntel Dem decries White House 'gag order' after Bannon testimony 'Total free-for-all' as Bannon clashes with Intel members Mellman: On Political Authenticity (Part 2) MORE immediately conceded the New Hampshire primary after media organizations quickly called the race for Sen. Bernie SandersBernard (Bernie) SandersMellman: On Political Authenticity (Part 2) Former Sanders campaign manager: Don't expect email list to be shared with DNC Adult film star: Trump and Stormy Daniels invited me to 'hang out' MORE (I-Vt.) on Tuesday.

The Clinton campaign conceded in a memo and said it was setting its sights on upcoming races in South Carolina and Nevada. Both are states where she holds a substantial lead.

"After splitting the first two contests, an outcome we've long anticipated, attention will inevitably focus on the next two of the 'early four states," Clinton campaign manager Robby Mook wrote in the memo.

"The nomination will very likely be won in March, not February, and we believe that Hillary Clinton is well positioned to build a strong – potentially insurmountable – delegate lead next month."

The Associated Press, MSNBC and CNN all called the race for Sanders as the final polls closed at 8 p.m. ET. The AP had only reported about 10 percent of the vote, with Sanders leading by a margin of 56 percent to 42 percent.

Sanders's win in New Hampshire had been expected — he came into Tuesday's primary with a substantial lead in the polls.

The bigger question for Democrats centers on his margin of victory.

The Sanders camp hopes that a definitive win can catapult him and narrow the gaps in both South Carolina and Nevada, where he trails the former first lady with minority voters. The Clinton team hopes to blunt his momentum by keeping the margin close.

The Clinton memo points at her "high levels of support in the African American and Hispanic communities" as proof that she has the edge over Sanders in a protracted Democratic primary fight.

It also argues that while Clinton has been in the public spotlight for years, media scrutiny of Sanders will only increase as the contest moves forward. 

This story was updated at 8:37 p.m.