pretext for its attack. we don't know exactly the form it will take. it could be a fabricated so-called terrorist bombing inside russia. the invented discovery of a mass grave. a staged drone strike against civilians. or a fake, even a real attack using chemical weapons. >> reporter: despite the dire warningly, blinken urged russia to engage in dialogue and diplomacy. >> let me be clear: i am here today not to start a war but to prevent one. >> reporter: but the russians took a different diplomatic approach, explging the second-ranking american official from the u.s. embassy in moscow, something u.s. officials called baseless. and in a written response to u.s. security proposals made last month, russia warned if the u.s. and nato don't agree to keep ukraine out of the military alliance, russia will be forced to respond with measures of a military, technical nature. also tonight, vice president harris is in germany for a major