Commentary Peace on Earth and goodwill to men this time of year seems increasingly absent in diverse places. In America the noble objective seems to have long ago left the U.S. Capitol where too many Members of Congress are as divided and angry at each other as ever. A new study by researchers at Cornell University finds there may be an actual “tipping point” where no issue imaginable can unite Republicans and Democrats. The study reveals that extreme polarization is so bad it may be irreversible. Worse, if that’s possible, the team’s predictive model for measuring the behavior of a polarized political group—like the current U.S. Senate—shows that even an attack by a foreign power or another pandemic would not heal the political divide. As Gerald Seib noted in a 2021 Year in Review column for The Wall Street Journal: “Neither party is strong enough to impose its will, while polarization has …