'I'm with her': President Obama endorses Hillary Clinton

President Barack Obama has formally endorsed Hillary Clinton for president of the United States. In a Clinton campaign video posted online, Obama said "I'm with her," echoing one of the campaign's slogans. (Scroll down to watch the video.)

Clinton became the presumptive Democratic nominee this week when she secured enough delegates to defeat Sen. Bernie Sanders.

"Look, I know how hard this job can be. That's why I know Hillary will be so good at it," Obama says in the video. "In fact, I don't think there's ever been someone so qualified to hold this office."

Once bitter rivals in the 2008 primary, Obama and Clinton worked to unify Democrats to defeat John McCain in that year's general election. Clinton then served as secretary of state during Obama's first term.

The Clinton campaign posted the video shortly after Obama met with Sanders at the White House. After that meeting, Sanders said he would stay in the primary race but would work to defeat presumptive GOP nominee Donald Trump in the fall.

Trump reacted to the endorsement via Twitter: "Obama just endorsed Crooked Hillary. He wants four more years of Obama—but nobody else does!" Clinton's social media team quickly retorted: "Delete your account."

Obama is set to campaign with Clinton in Wisconsin next week according to reports.