Who expressed concern that political parties were a threat to the ability of people in government to work together?

George Washington said it.

The correct answer to this open question is the following.

It was President George Washington who expressed concern that political parties were a threat to the ability of people in government to work together.

Indeed, President Washington was against the creation of political parties and factions because he believed this was a reason to split the nation. Some Americans would support one faction while others would support another faction. He witnessed how federalists and antifederalists debated during the Constitutional Convention in Philadelphia, Pennsylvania, from May to September 1787.