It is possible that the good guys knew about this train attack, and let it happen but under controlled circumstances, to minimize the damage so nobody on the train would be hurt.
They probably have evidence of the bad guys planning this & carrying it out, and the attempt is all over the news now. This can be used as another convincing proof in the list of bad guy actions, when POTUS reveals all.
It wouldn't be as convincing if POTUS claims "The deep state was going to wreck a train of 100 republicans, but we made sure nothing happened so you never heard about it."