A couple of weeks before the primary, the Christian Coalition of Colorado sent out a direct mail piece claiming that Lamborn's main opponent, Jeff Crank, was a mouthpiece for the homosexual lobby. Several of Lamborn's staff resigned over these mailings and the national brank of the CC apologized and decried the ads. Coincidentally, the head of the Colorado branch of the Christian Coalition is the brother of Lamborn's campaign manager. Odd coincidence that.
The ads drew a lot of backlash against Lamborn and since these mailings came out after the absentee ballots were sent in, many feel that Lamborn would have lost if the voters had seen the ads earlier.
As for the "RINO" tag, Crank had the endorsement of outgoing representative Joel Hefley and Tom Tancredo, so that as you will.
(BTW: In interest of full disclosure, I live outside this district, so I don't have a dog in this fight.)
Sigh. So *take* that as you will.