Washington (CNN) President Barack Obama's chief of staff is crediting Vermont Sen. Bernie Sanders with "some movement" on guns in recent days -- and made clear Obama is watching closely.

In an interview with CNN's Jake Tapper on "State of the Union" Sunday, White House chief of staff Denis McDonough credited Sanders for shifting to the left on gun control.

"As it relates to Sen. Sanders, we've seen some movement on this since the op-ed appeared on Thursday. We think that's good. If that continues, that's the goal of this, is making sure that we have gun laws that are responsive to the wishes of the American people, not responsive to the big NRA bosses here in Washington," McDonough said.

Obama said in a New York Times op-ed that he won't campaign for or vote for anyone -- Democrat or Republican -- who doesn't support "common-sense gun reform."

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