Partisanship is the lifeblood of democracy, but it also has harmful effects that can be especially damaging to foreign policy. Politicians are entrepreneurs seeking markets, so there is always someone willing to become the advocate of any position for which there is a constituency. Such behavior can be craven, but it guarantees that all elements of the citizenry will find their champions.
"Ambition must be made to counteract ambition," said the Founding Fathers, meaning that this competition within the government would prevent a concentration of power that could threaten the liberties of citizens. The founders distrusted parties, which they called "factions," but history has shown that the contest between parties is no less an important mechanism for keeping government limited than is the separation of powers between branches of government.
Nonetheless, although exaggerated, the founders' fear of "faction" has not proved entirely fatuous. Just as democracy must embody a mix between leadership and representation, so it must also include elements of principle and concern for the commonwealth as well as personal ambition. Partisanship sometimes elevates ambition too far over principle, hardening divisions and impeding compromise.