Sen. John Ensign (R-NV) isn't off the hook for last year's scandal-laden affair with his staffer's wife. In fact, his troubles now look worse than ever.

The Nevada television news station KLAS reported on Thursday that the Department of Justice has enhanced its "criminal" investigation of the events surrounding Ensign's actions.

The criminal probe stems from a romantic affair Ensign had with the wife of his key staffer and close friend, Doug Hampton, and what Ensign has done to help Hampton financially.

Subpoenas have been issued to at least six Las Vegas businesses. The Justice Department came to Las Vegas to interview several prominent business and political figures in what appears to be a wide-ranging and deadly-serious criminal probe.

The subpoena, which can be read here, seeks "any and all records; including emails, phone calls and calendars regarding any interaction the Las Vegas businesses may have had with Ensign, his Chief of Staff John Lopez, Doug Hampton, Hampton's wife Cindy -- the object of the senator's romantic interest -- Ensign's principal political advisor Mike Slanker, and Slanker's company November Inc," according to KLAS's Web site.

Talking Points Memo's Zachary Roth notes that "the federal grand jury probe of the sex-and-lobbying scandal that ensnared Sen. John Ensign (R-NV) is getting hotter than a Las Vegas parking lot in July."

The Associated Press provides details on the nature of the investigations against the Nevada senator, who was reportedly mulling a run for president in 2012 prior to these transgressions becoming public.

According to one subpoena obtained by a Las Vegas television station, recipients were ordered to testify March 31 in Washington, D.C., and to turn over documents relating to the Republican senator.

The FBI and Senate Ethics Committee are investigating whether Ensign tried to limit political damage from an affair he had with the wife of one of his Senate aides by conspiring to help the aide find a new job as a lobbyist, which might have violated restrictions on lobbying by former congressional staff.

Federal criminal law prohibits congressional aides from lobbying their ex-bosses or office colleagues for one year after departing their Hill jobs. Ensign acknowledged the relationship with Cynthia Hampton last June. In addition to Ensign's helping her husband, Doug Hampton, gain employment with a lobbying firm, Ensign's parents provided the Hamptons with a payment of $96,000 that they described as a gift.

The Washington Monthly's Steve Benen offers additional background on the situation.

If you're just joining us, Ensign's humiliation came to public attention in June, when we learned the conservative, "family-values" lawmaker carried on a lengthy extra-marital affair with one of his aides, who happened to be married to another one of his aides. Ensign's parents tried to pay off the mistress' family.

The scandal grew far worse in October, when we learned that the Republican senator pushed his political and corporate allies to give lobbying contracts to his mistress's husband. When Douglas and Cynthia Hampton left Ensign's employ -- because, you know, the senator was sleeping with Cynthia -- Ensign allegedly took steps to help them make up the lost income, leaning on corporate associates to hire Douglas as a lobbyist. Emails that surfaced last week bolstered the allegations.

Ensign has denied that he violated any ethics laws and has pledged to cooperate with the investigations.

It sounds like the federal grand jury probe of the sex-and-lobbying  scandal that ensnared Sen. John Ensign (R-NV) is getting hotter than a  Las Vegas parking lot in July.