A “flip-flop” is a sudden reversal of opinion or policy by a politician, usually running for office.
NPR notes the term “has been a fixture in popular American parlance at least since the 1880s. A New York Tribune writer in 1888 called out President Grover Cleveland for his ‘Fisheries flip-flop,’ presumably referring to Cleveland’s handling of the fishery treaty that governed waters shared by American and Canadian vessels and perhaps making wordplay on the way fish flop and flip on a boat deck. And in 1892, the New York Times pointed to the ‘flip-flop antics’ of John Boyd Thacher, the once-and-future mayor of Albany.”
Matthew Cooper: “Somewhere along the way, the charge of flip-flopping became one of the deadliest in politics—the shorthand for a lack of character. By contrast, a politician who didn’t change his or her mind, or who vowed to be uninterested in polls, was considered to be of a higher caliber. But there is a case for flip-flopping, or what might be called being human. After all, almost anyone with common sense has probably evolved on some position or another.”