Bernie Sanders outraised Hillary Clinton in January

Hillary Clinton announced Thursday that she raised $15 million for the Democratic nomination contest in January, falling behind rival Bernie Sanders for the first time in their battle for the White House.

Sanders previously announced he had collected an eye-popping $20 million last month, and Clinton's aides had warned reporters and supporters that Sanders had the fundraising advantage as the two candidates head into New Hampshire's Feb. 9 primary.

Even so, Clinton officials said the campaign saw some of its strongest grass-roots fundraising days in January and now has collected money from more than 670,000 people around the country.

"We have the resources we need to take the fight to New Hampshire, Nevada, South Carolina and beyond," Clinton campaign manager Robby Mook said in a news release.

In addition to the $15 million to her campaign, Clinton raised $5 million for the Democratic National Committee and state parties last month, campaign aides said. The party money can only be used to help the eventual nominee.

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Bernie Sanders raises $20 million in January

Clinton's camp has sounded alarms about Sanders' blistering fundraising pace. On Wednesday, the Vermont senator said he had collected another $3 million following his razor-thin, second-place finish in Monday's Iowa caucuses.

That prompted this Wednesday night email from Mook with the subject line: "Bernie raised $3 million in 24 hours."

"You've probably heard by now, but let me say it again… WE WON THE IOWA CAUCUS!

Now take that enthusiasm and channel it, because we've got our work cut out for us: Bernie's supporters chipped in $3 million within 24 hours of the caucus. That's an incredible show of support, and we need to make sure we're fighting just as hard for Hillary. Can you chip in $1 now to help us close the gap?"