Politics ends at the water’s edge
The phrase politics ends at the water’s edge means that when it comes to foreign affairs, the US is united and bipartisan. It discourages lawmakers who are traveling overseas from making comments that criticize the president or from sending mixed messages about his foreign policy.
The phrase was coined in 1947 by Republican Sen. Arthur Vandenberg, then the Senate Foreign Relations Committee chairman, as he urged bipartisanship with President Harry Truman, a democrat, in support for the Truman Doctrine, the Marshall Plan, and NATO.
In 2017, this phrase took an interesting turn. Within the Trump administration, there seems to be some discord regarding foreign policy among the president, Secretary of State Rex Tillerson, and Defense Secretary James Mattis.