In response to the potential that Trump will basically not make use of diplomatic apparatus, which tends to be much cheaper than bombs in both the short run and long run in most matters of foreign affairs, key figures in the US Senate have been running a sort of parallel State Department on their own initiative.
This is mentioned in a NYT article where Trump’s decision to hand authority over troop deployment activities directly to the Pentagon in addition to the cuts he wants to the State Department seem to be meeting a response of Congress “to recapture much of the Senate prerogatives on foreign policy”.
It is worth mentioning that the (at least temporary) blockage of some additional arms sales to Saudi Arabia is said to be tied to concern for the high level of civilian casualties caused by Saudi use of lethal force in Yemen.
Anyone know any place outside of the West where non-presidents who don’t agree with the president can take their elected representative “stamps” and go do quasi-foreign policy quasi-independently? (The example of Chrystia Freeland in Canada doing an independent fact-finding mission to Ukraine while in opposition is another interesting example along those lines.) A Chinese mayor, for example, might independently seek city-to-city relations in a foreign place, but how long do you think he’d be in the mayorship after his return if it turned out that a major objective in a particular visit was to promote courses of action that differed significantly from (in particular if contradicting) those sought by the president?