Secretary of State John KerryJohn Forbes KerryOcasio-Cortez and Cruz's dialogue shows common ground isn't just for moderates 'Landslide' for Biden? A look at 40 years of inaccurate presidential polls Trump campaign considering making a play for blue state Oregon: report MORE said Sunday that a new deal with Russia to revive a crumbling cease-fire in Syria is not based on trust. 

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"Nothing we talked about is based on trust," Kerry said on NBC's "Meet the Press." 

"I'm not sitting here naively trusting what the Russians may or may not do. What we have done is laid out a series of steps concretely. Each step is the preclude to something else happening. If it doesn't happen, then there won't be that progress," Kerry said. 

A proposal obtained by The Washington Post calls for the U.S. and Russia to collaborate militarily against Jabhat al-Nusra, al Qaeda’s affiliate in Syria. In return, the proposal would require that the Syrian air force be largely grounded.

Few details of the partnership have been released, Kerry said, because he doesn't want to "raise expectations."

"I'm trying to lay this out in a way that is between us on a basis of steps taken. This has to be proven step by step, and if it's proven, it has the potential of changing the dynamics on the ground," Kerry said.