Final answer:
George Washington's sentence warning about political parties states that they may become a tool for unprincipled individuals to seize control of the government and undermine the people's power.
Step-by-step explanation:
The specific sentence from George Washington's Farewell Address that warns Americans against the negative impact of political parties is:
"However, combinations or associations of the above description may now and then answer popular ends, they are likely, in the course of time and things, to become potent engines, by which cunning, ambitious, and unprincipled men will be enabled to subvert the power of the people and to usurp for themselves the reins of government, destroying afterwards the very engines which have lifted them to unjust dominion."
This sentence encapsulates Washington's concern about the potential for political parties to enable individuals with self-serving interests to gain power and to threaten the democratic foundations of the nation.