numbers will take part in the earlier so-called undercard debate. more now on the final preparations and also what s at stake tonight. nbc s peter alexander reports from the site of tonight s debate, the reagan presidential library in simi valley, california. reporter: alex, good morning from simi valley. the spotlight will again shine brightly on donald trump but also on some of his challengers, note notably ben carson and carly fiorina. jeb bush and scott walker have seen their pollplummet. a bad performance tonight for a candidate could mean the end of the road. breaking out the big guns ahead of tonight s debate, republican front-runner donald trump revved up supporters on the uss iowa in los angeles. delivering a speech heavy on promises, but light on specifics. we re going to come out with some plans in a very short time. we re going to be building up our military. reporter: earlier predicting a barrage of attacks from his republican rivals. you know, they re