By STEPHEN BRAUNWASHINGTON (AP) â¿¿ Sen. Robert Menendez sponsored legislation with incentives for natural gas vehicle conversions that would benefit the biggest political donor to his re-election, the same eye doctor whose private jet Menendez used for two personal trips to the Dominican Republic, an Associated Press investigation found. The disclosure reflects the latest intersection between the New Jersey Democrat who is the subject of an ethics inquiry on Capitol Hill and the Florida doctor involved in a federal criminal investigation. Dr. Salomon Melgen invested in Gaseous Fuel Systems Corp. of Weston, Fla., and joined its board of directors in early 2010, according to the company's chief executive and a former company consultant. GFS, as the company is known, designs, manufactures and sells products to convert diesel-fuel fleets to natural gas. The amount of Melgen's investment is confidential under rules of the Securities and Exchange Commission, but a 2009 document filed with the SEC showed the company required a minimum individual investment at that time of $51,500. Menendez was a principal supporter of a natural gas bill from 2009 through 2012 that would boost tax credits and grants to truck and heavy vehicle fleets that converted to alternative fuels. The bill stalled in the Senate Finance Committee, and after it was revived in 2012, the NAT GAS Act failed to win the needed 60 votes to advance. While the bill was under consideration between 2009 and 2011, the former consultant for GFS spent $220,000 lobbying Menendez's staff and other congressional and federal officials on the act's provisions as well as other regulatory issues, according to interviews and Senate records. There is no evidence that Menendez offered direct help or intervened on behalf of the company or Melgen. Instead, the connection between the two men's interests in natural gas is the latest example of the close symmetry between the senator â¿¿ who recently rose to become chairman of the Senate Foreign Relations Committee â¿¿ and his millionaire backer. It illustrates the way Menendez's political clout has at times overlapped with Melgen's financial investments.