Fred Thompson's one-time New Hampshire primary adviser, Dan Hughes, who for a time was identified as the campaign's state chairman, has resigned and thrown his support behind Arizona Sen. John McCain for president.

Hughes is now the vice chairman of the McCain New Hampshire operation. He showed up Tuesday with McCain for the official filing of paperwork to participate in the New Hampshire primary.

Hughes quit Thompson's team three days ago, and privately sources close to the Thompson campaign say the campaign had its differences with Hughes.

Hughes told FOX News that Thompson is not organizing in any way that indicates a serious candidacy and McCain is the "real deal."

Thompson was in Naples, Fla. Tuesday to offer his plan for reforming immigration policy.

FOX News' Carl Cameron contributed to this report.