Although a half-dozen Republicans have now filed for Oklahoma’s 5th district open seat, three GOP frontrunners have emerged and it’s a safe bet that two of those three will meet in an August 2010 primary runoff.

One of those two runoff contenders could well be state Corporation Commissioner Jeff Cloud, who joined the race late last week.

“I’ve started campaigning a little bit here and raising money so the campaign is getting started,— Cloud said Thursday after submitting his paperwork to the Federal Election Commission.

Cloud — who was re-elected in 2008 to a second six-year term on the corporation commission and also was a staffer for former Rep. J.C. Watts (R-Okla.) — said he’d be making a formal campaign announcement in the next week and a half.

Cloud’s main competition in the Republican primary appears to be state Rep. Mike Thompson and former state Rep. Kevin Calvey, who ran in the GOP primary when the district was last an open-seat race in 2006. That election was won by then-Lt. Gov. Mary Fallin (R), who is leaving the House to run for governor.

While Cloud waited to make his decision until Oklahoma City Mayor Mick Cornett (R) — who lost a 2006 GOP runoff to Fallin and was viewed as the early favorite this time — passed on the contest in late August, both Calvey and Thompson filed in the early spring. That allowed both men to amass impressive war chests with nine months to go before the July primary.

Thompson raised $201,000 from July to September and ended last month with about $303,000 in cash on hand.

Calvey raised about $148,000 in the third quarter and reported $374,000 in the bank as of Sept. 30.

Key to Calvey’s fundraising success has been support from the anti-tax group Club for Growth. Calvey was the first Congressional candidate of the 2010 cycle that the club endorsed and that support helped Calvey bring in more than $45,000 in bundled contributions during the third quarter. (The club also endorsed Calvey in 2006, when he finished fourth in a multi-candidate primary.)

Calvey campaign consultant Trebor Worthen said Cloud’s entry into the race doesn’t change Calvey’s campaign strategy.

“Kevin Calvey is still the leading conservative candidate with the support of national and local taxpayer organizations and veteran organizations,— Worthen said.

A major part of Thompson’s fundraising has come from the Oklahoma business community, especially the oil and gas industry.

Now that Cloud is in the race, it will be interesting to see if he can wrestle some of that support away from Thompson.

Cloud doesn’t have to give up his seat on the corporation commission to run for Congress and he also serves as a member of the Electricity Committee for the National Association of Regulatory Utility Commissioners and as a member of the Legal and Regulatory Committee of the Interstate Oil and Gas Compact Commission.

“A lot of the big money in this district is committed, [but] that’s not to say they won’t play both ways now. … Energy guys know who [Cloud] is and the energy guys have a lot of money,— one Oklahoma Republican insider said.

Supporters say the energy community will take a second look at the race now that Cloud is in, and while it’s unclear whether Cornett will get involved in the contest personally, some of Cornett’s close advisers are backing Cloud.

One person who isn’t likely to get involved in the race is Fallin, who won the seat in 2006 after Cornett took her to a runoff. In the primary that year, Calvey took 10 percent.

Urologist Johnny Roy, who also ran in 2006, is also back for another shot at the GOP nomination and he reported about $31,000 in cash on hand at the end of September. Other GOP candidates include youth camp director James Lankford, who ended September with about $53,000 in the bank, and Navy veteran Rick Flanigan.

Sen. John McCain (R-Ariz.) won the district by 18 points in last year’s presidential race, so the Republican primary is likely going to be the only contest that will matter next year. There has been some idle chatter about Oklahoma first lady Kim Henry (D) running for the seat next year, but there is no evidence that she is seriously considering a bid.