From left, Senators Jeanne Shaheen, John Curtis, Thom Tillis and Jacky Rosen in Taiwan in March. All four signed a letter to President Trump urging him to move forward with the Taiwan arms sale.
For the fourth time since the war began, G.O.P. senators successfully fended off an effort to constrain the president. But there were signs of growing unease among Republicans.
The chair of the National Transportation Safety Board warned that a provision in the new defense bill would worsen the risk of midair collisions near the Washington-area airport where a deadly crash in January killed 67 people.