Republican Scott McInnis has decided he will not run for the U.S. Senate next year, removing one of the highest-profile GOP names from what is sure to be a hotly contested race.McInnis had formed an exploratory committee just last month after Republican Sen. Wayne Allard announced he would not seek a third term. But McInnis said he decided against it after considering what was best for Colorado and for his family."I will remain actively involved, just not on the ballot," he said in a written release.At least two other Republicans said Wednesday they are still considering running: former congressman Bob Schaffer and Attorney General John Suthers. Democrat Mark Udall, a congressman who represents Boulder, has not made a formal announcement but has said he will run for the seat.Because the seat will be open in 2008 and control of the Senate will be up for grabs, the race is expected to be fierce. Some analysts have said candidates could spend a total of $20 million, which would make it the most expensive in state history.Schaffer ran for the GOP nomination for Senate in 2004 but was beaten beer executive Peter Coors, who was recruited by then-Gov. Bill Owens to run. Coors lost to Democrat Ken Salazar.Schaffer said he believes voters lurched to the left in 2006 when the GOP lost two key Colorado positions to Democrats, the governorship and a seat in Congress, both of which were open. He said voters may be ready to go the other way next year."That's what I'm evaluating, whether the pendulum will swing back to the center, which would give Republicans an advantage," he said.Nate Strauch, a spokesman for Suthers, said the attorney general also is evaluating the race."He hasn't ruled out a run, but he's not in the race at this point," Strauch said.Republican state chairman Dick Wadhams said a number of Republicans are considering the race and predicted it will sort itself out soon.Colorado State University political science professor John Straayer said Udall will be a formidable opponent because he is well-known across the state.Udall is also a member of one of the West's best-known political families. His father, Morris, represented Arizona for three decades in the U.S. House; his uncle, Stewart, was a three-term Arizona congressman and became interior secretary in 1961; and his cousin, Tom Udall, is a Democratic congressman from New Mexico.But "I don't think he's invincible," Straayer said. "Wadhams knows how to spell 'Boulder' and he knows how to spell 'liberal.'"Straayer said Schaffer is associated with the religious right but Republicans will find it difficult to reject him as they did in 2004 because of Coors' loss to Salazar."They scrambled to find an alternative candidate, and they lost," Straayer said.Straayer said Suthers has had less experience with statewide races.State Democratic Party chairwoman Pat Waak said McInnis' decision to withdraw "may give a signal that Colorado Republicans are not interested in moderate candidates."She said McInnis has a history of voting against a gay marriage ban."If that is the reasoning behind his announcement, it is sad that the Republican Party still doesn't understand that the state, and the country, is looking for solutions, not ideologies," Waak said.McInnis represented the sprawling 3rd Congressional District in the western and southern parts of the state from 1993 to 2005. He has about $900,000 left over from his congressional campaign fund, which could have been used in his bid to replace Allard.He currently works as a lawyer for Hogan and Hartson in Denver.