Obviously, Benedict Arnold is a person’s name, but it is also used as an idiom. We will examine the meaning of the idiom Benedict Arnold, where it came from, and some examples of its use in sentences
A Benedict Arnold is a traitor, someone who has been revered or been elevated to a place of trust and has betrayed that trust. The idiom Benedict Arnold is an American term and has been in use since shortly after the Revolutionary War. The idiom Benedict Arnold is derived from a very real person who was a general for the Americans during the Revolutionary War. Benedict Arnold was born in the Connecticut Colony in 1741 and fought in the French and Indian War for a very brief period when still in his teens. He became a successful apothecary, continuing to conduct business in defiance of the Sugar Act and the Stamp Act. He joined the fight for independence against Britain and King George III as a captain in the militia, taking part in the siege of Boston that occurred after the Battles of Lexington and Concord and helping Ethan Allen and the Green Mountain Boys to capture Fort Ticonderoga and Fort Saint-Jean. He went on to attack Quebec and take part in the Saratoga campaign. He was promoted to major general, but still felt that he did not receive the recognition that he deserved. When serving as military governor of Philadelphia, he was accused of misusing his office. Eventually, debt-ridden and bitter, he spied for Britain and agreed to turn over the fort at West Point to the British for twenty thousand pounds, a fortune by today’s standards. Unfortunately for Arnold, the plot was uncovered and he was forced to flee. Though Arnold was guilty of treason, he was never brought to justice. The idiom Benedict Arnold, which has been in use since at least 1806, is still a stinging accusation in American English. Note that both words are capitalized, as it is a proper name.
I’m sure there are probably those among Trump’s most ardent supporters who consider Scaramucci equivalent to a modern-day Benedict Arnold. (The Boca Raton Tribune)
Mayes’ call for a more moderate tone, as well as his 2017 work with Democrats to extend the state’s cap-and-trade pollution-fighting program, earned him a ‘Benedict Arnold’ label from California conservatives loyal to Trump. (The Press-Enterprise)
The son of two immigrants from the Middle East, he has been called a Democrat, “Al Qaeda’s best friend,” and a “Benedict Arnold against the Constitution.” (The New Republic)