In an interview, Mr. Rubio described Mr. Braman as a father figure who had given him advice on everything from what books to read to how to manage a staff. After Mr. Rubio’s father died in 2010, Mr. Braman called every other day to check in.

Pressed on his financial ties to Mr. Braman, Mr. Rubio said in an interview that he saw no ethical issue. “What is the conflict?” he asked. “I don’t ever recall Norman Braman ever asking for anything for himself.”

He acknowledged that Mr. Braman had approached him about state aid for projects, such as funding for cancer research, but said that he had supported the proposals on their merits.

The reliance on Mr. Braman is likely to put a spotlight on the finances of Mr. Rubio, who ranks among the least-wealthy candidates in the emerging Republican field. Mr. Rubio left the Florida House of Representatives in 2008 with a net worth of $8,351, multiple mortgages and $115,000 in student debt. In his latest financial disclosure form, for 2013, he reported at least $450,000 in liabilities, including two mortgages and a line of credit.

Mr. Braman and aides to Mr. Rubio have declined to say how much personal financial assistance he has provided to Mr. Rubio and his wife, directly or indirectly, but it appears to total in the hundreds of thousands of dollars.

In a series of interviews at his office in downtown Miami, above showrooms of shiny BMWs and Rolls-Royces (he also sells Cadillacs, Audis and Bugattis), Mr. Braman praised the Rubios. He recounted what he described as “excellent service from them” over the years, and said he wanted nothing in return for his financial help.