Sen. Craig Thomas (R-Wyo.) passed away Monday night at National Naval Medical Center in Bethesda, Md., after a seven-month bout with leukemia. He was 74.

According to a statement from Thomas’ family, the Senator died with his wife, Susan, his sons, Patrick and Greg, and daughter, Lexie, by his side. His death quickly brought forth statements of sympathy from his colleagues.

“Wyoming had no greater advocate, taxpayers had no greater watchdog and rural America had no greater defender than Craig Thomas,” said Senate Minority Leader Mitch McConnell (R-Ky.). “The Senate is a lesser place without Craig here, but the state of Wyoming and our nation are much better places because he was here.”

Earlier Monday evening, Thomas had undergone a second round of chemotherapy and fought infection related to his struggle with leukemia. A statement from the Senator’s family indicated the medical team was having difficulty managing his blood cancer. Thomas was hospitalized on May 24 following routine tests to monitor his bone marrow and white and red blood cell counts.

Thomas was first diagnosed with acute myeloid leukemia in November 2006, just after sailing to a third Senate term with 70 percent of the vote. The popular Wyoming Republican began his treatment within days after learning of his condition, and continued his therapies throughout the early part of the 110th Congress.

Doctors felt Thomas was having such a positive response to the treatment that they opted against administering a round of chemotherapy in March, Thomas’ office said. Meantime, Thomas was back to a regular vote and committee schedule in the Senate and continued to voice optimism about his recovery.

“When these things happen, you have to do what’s necessary to deal with it,” Thomas said in a January interview with Roll Call. “I must say I didn’t know what I was getting into. I was shocked and concerned because anything compared with that title is scary. I just look forward to getting back in the swing of things.”

Thomas said then that he was surprised when his cancer diagnosis came down since he had little forewarning and no one in his family has suffered from the malady. Initially, the doctors believed it was pneumonia.

Wyoming law ensures that Senate Republicans will not lose a vote, as Gov. Dave Freudenthal (D) is required to select a replacement for the Senator from among three candidates submitted to him by the state GOP.

However, the individual chosen by the governor to fill the remainder of Thomas’ term will only serve until November 2008, giving the seriously threatened Senate Republican Conference another seat to protect in a cycle when they already are defending nearly twice as many seats as the Democrats.

Senate Democrats are defending only 12 seats this cycle, compared to a whopping 21 for the Republicans.

Before Thomas passed away Monday, Wyoming Republican Party Chairman Fred Parady confirmed that the 71-member state GOP central committee would select the names of three individuals from which Freudenthal would choose a successor.

But Parady said the state GOP has yet to work out the mechanics of how those individuals would be chosen, saying he hopes it doesn’t become necessary.

“We’ll deal with an opening when and if it occurs. We hope it doesn’t,” Parady said Monday afternoon.

Wyoming law mandates that the governor is to inform the state GOP immediately upon being notified in writing that a Senate seat has become vacant. The governor is then required to notify the political party of the vacated Senator, which upon receiving a written notice from the governor, has 15 days to call a meeting of its central committee and come up with three names that meet the legal requirements to serve as a Senator.

Once the governor receives those three names, he has five days to choose one of them for the vacancy, and that choice would then serve until the next regularly scheduled general election.

Previously a state legislator, Thomas was first elected to the House in 1989, winning a special election to replace then-Rep. Dick Cheney (R-Wyo.) who resigned to become Defense Secretary. Thomas successfully ran for the Senate in 1994, and won re-election to the seat in 2000 and again last year.

Thomas, an ally of Cheney with strong agricultural roots, was twice mentioned as a possible Interior secretary, including last year when Gale Norton announced she was leaving the Bush administration post. Thomas later withdrew his name from consideration, and Dirk Kempthorne (R), the former Idaho governor, won the appointment.