Former President Barack Obama once warned he would intervene to stop Sen. Bernie Sanders, I-Vt., from winning the Democratic presidential nomination, according to a new report that sheds light on Obama's personal views of the jam-packed primary field with no clear front-runner.

Obama has largely stayed on the sidelines to date, refraining from any endorsements though he has issued general warnings to the party to avoid calls for radical upheaval in their policy pitches. These warnings were seen as a swipe at candidates like Sens. Elizabeth Warren, D-Mass., and Sanders.

But a new Politico Magazine report gives a clearer picture of what Obama is worried about -- claiming he has said in private he'd speak out against Sanders if it looked like he could actually win...

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