Why does George Washington support the Constitution? To what does “a Constitutional door is left open” refer?

Answer 1

President Washington was in favor of a strong national government.

http://www.mountvernon.org/research-collections/digital-encyclopedia/article/ratification-of-the-constitution/

He especially pointed to the Constitutional Amendment process to make changes as necessary.

http://books.google.com/books?id=A0YMCgAAQBAJ&pg=PR18&lpg=PR18&dq=a+Constitutional+door+is+left+open%E2%80%9D&source=bl&ots=hYJMmXlezD&sig=5XTZafGKWY-iMAn2ZgktCb1av2E&hl=en&sa=X&ved=0CFAQ6AEwCWoVChMIte_cvavCxwIVg1w-Ch2L3gQg#v=onepage&q=a%20Constitutional%20door%20is%20left%20open%E2%80%9D&f=false

Answer 2

George Washington and the Constitution:

http://www.shmoop.com/george-washington/constitution.html

As to the quotation, who said it and when?