U.S. Sen. Robert Menendez will resign effective Aug. 20 in the wake of being convicted on federal bribery and corruption charges, a source with knowledge of the situation said. His decision formally ends a decades-long political career that saw the New Jersey Democrat gradually rise to the highest ranks of American government before rapidly plummeting over the last year. Menendez maintained his innocence and repeatedly refused to step down from the Senate seat he has held since 2006 even after he was indicted last September and many top Democrats from Trenton to D.C. called for him to leave. B…