« For years, Mr. Biden has been fond of saying that “this is not your father’s Republican Party” to highlight the G.O.P.’s rightward drift. But the consensus-seeking former senator was loath to paint with too broad a brush.

Informal conversations with historians helped change his mind.

The historians explained to Mr. Biden the power of labels and how they had been used in the past to successfully confront far-right factions, helping him gain comfort in publicly tagging Republican extremism as “MAGA Republicans,” according to a White House official who discussed the issue with him. A study by Biden allies identified “MAGA” as the most effective label — a phrase connoting “extreme,” “power-hungry” and “radical” for some voters. »