captioning sponsored by cbs diaz: tonight, battlefield struggles. ukraine says russia s latest ve is t succeeding as concern rises about the country s radioactive risk. reporter: i m chris livesay in ukraine, where the president warns the threat of a nuclear disaster remains high. diaz: also tonight, a tornado tears through kansas, the damage widespread, the strong storms now threatening millions from arkansas to wisconsin. plus, wall street woes. markets plunge on economic fears. today, warren buffett compares financial advisers to gamblers. reporter: i m michael george on wall street. stocks take a dive, ramping up fear over the economy.