In the coming days, the Senate Foreign Relations Committee will move after years of resistance to draft a new war authorization to fight the Islamic State, asserting more power over troop deployments as Mr. Trump publicly cedes that authority to the Pentagon.

Not least, the Trump administration’s budget request that would gut the State Department was met by an instant rebuke from Senator Mitch McConnell of Kentucky, the majority leader, who won’t even consider it.

In the meantime, a number of senators have formed a kind of parallel operation to the State Department by visiting allies to assure them of America’s commitments.