The phrase "a more perfect union" is drawn from the Preamble to the Constitution of the United States of America. The complete preamble reads: We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.
The preamble sets forth a statement of the vision of the newly formed United States of America that will be embodied in the Constitution.
The bridge that Shaw and Greer sit by is the same bridge in The Girl on the Train (2016).