very much. foreign policy analysts say the threat by north korea is a familiar ploy, raise expectations, threaten to cancel talks and push for more concessions. sam, the summit could still happen. this is certainly mott the first time hopes of a breakthrough with north korea have run into trouble. walk us through some of the past efforts. >> reporter: thanks, wolf. to quote sarah sanders, we should expect a cycle of north korean prove case and violation. in 1994, we signed the agreed framework with north korea after they engineered a crisis. north korea announced 18 months before sign thing agreement they were withdrawing from the nuclear nonproliferation treaty. under this agreement, we did get our first freeze with north korea. they agreed to freeze construction and operation of nuclear reactors in exchange of some concessions from us.