Rep. Alexandria Ocasio-Cortez, D-N.Y., a 35-year-old member of the progressive “squad” who is often mentioned as a future presidential hopeful, is taking on a more senior colleague, Rep. Gerry Connolly, D-Va., 74, who is battling esophageal cancer and was just elected to his ninth term.“If she wins, it’s the end of seniority,” said a House Democrat who has served decades in Congress.