Sen. Robert Menendez, the only U.S. senator to be indicted twice, is slated to step down today. It will end a decades-long political career that saw the New Jersey Democrat rise to the highest ranks of American government before rapidly plummeting over the last year in the midst of astounding charges of gold-bar bribes. After he was convicted last month on federal corruption charges and faced expulsion from Congress, Menendez announced he would resign effective Aug. 20. Gov. Phil Murphy has temporarily appointed his long-time ally and former Chief of staff George Helmy to the seat, while an el…