Here was Mark Levin in 2008 arguing that Romney was the most conservative choice:
Of course that was before Levin suddenly decided to hate Romney's guts. In 2008 he was calling Romney a conservative... maybe an imperfect conservative, but still a conservative. And now Romney is some sort of ultra-liberal who should be hated like poison?Let’s face it, none of the candidates are perfect. They never are. But McCain is the least perfect of the viable candidates. The only one left standing who can honestly be said to share most of our conservative principles is Mitt Romney. I say this as someone who has not been an active Romney supporter. If conservatives don’t unite behind Romney at this stage, and become vocal in their support for him, then they will get McCain as their Republican nominee and probably a Democrat president. And in either case, we will have a deeply flawed president.
Well, I don't see any perfect conservatives this time around either. I initially supported Rick Perry, but he just wasn't able to sell himself... so now that Perry is gone, Romney has become my second choice. Who else am I supposed to vote for? Rick Santorum may yet win the nomination, and I will vote for him if he does, but I don't see how he could possibly beat Obama in the general election. (I don't think that Newt Gingrich could beat Obama either, but I don't see him winning the nomination at this point anyway, so the question is probably moot.)
As our nominee, Mitt Romney would keep the focus on Obama's failed policies... Romneycare is a problem for Romney, but not an insurmountable one. I think Romney will do a much better job of exposing Obama as a radical leftist than Santorum ever could, mainly because Santorum is too eager to let himself get lured into lecturing us about things like Satan, sodomy, pornography, contraception, and whether or not Protestants are real Christians.
I've been fairly impressed with Mitt Romney's performance in the debates so far, and I think he would do just fine against Obama... but you don't have to take my word for it, here is Santorum himself endorsing Mitt Romney in 2008: