If they obtained info about this through their role as a senator/congressperson, and not just through normal channels. If I understand it correctly:

Insider trading off of classified or whatever info they get from their senate/congress job - not illegal (though imo it should be illegal). (Edit: as mandevil points out, strictly speaking illegal, but largely uneforceable/unenforced)

Insider trading off of info they got from their buddy at XYZ place who knew about something ahead of time, unrelated to their senate/congress job - still illegal, same as for other people.