Under the procedures of The Railway Labor Act, at this stage of the proceedings the president no longer has any power (except as mentioned in the next paragraph). He used the power that he does have earlier, when he ordered a "cooling off" period and the establishment of a Presidential Emergency Board to hear both sides and make recommendations.
Now, it's up to the Congress. If there's a strike, they can either pass legislation ordering the unions back to work (which I believe the president must sign), or even impose a settlement (I believe this is done via legislation, again the president must sign).
So it's up to the Congress now.
For the leftists to force the rail unions back to work... not going to look so good with elections so close.
But once you get out of the urban areas, a surprisingly high number of unionized rail employees are of "the deplorable class", if you get my meaning...