By DÁNICA COTO, Associated Press SAN JUAN, Puerto Rico (AP) — The two parties that have dominated Puerto Rican politics for decades are losing their grip as they face the stiffest competition yet from a younger generation fed up with the island’s corruption, chronic power outages and mismanagement of public funds. For the first time in the island’s governor’s race, a third-party candidate has a powerful second lead in the polls ahead of the U.S.