Some people on the right have it in their heads that Obama winning the White House has somehow fundamentally changed the nature of politics itself. I know Obama said he wanted to "fundamentally transform" the country, but I really don't think he's changed the way the GOP will win elections.
Obama's victories in 2008 and 2012 hasn't changed the fact
that it's been nearly 100 years since a Republican senator has won in a
presidential election. Obama could get away with being a presidential candidate that had an impossibly thin record and the most inane slogans you could ever imagine because the media chose to treat him like a demigod anyway. Republicans don't have the luxury of being worshipped by the media. The media only ever gives Republicans glowing coverage when those Republicans are bashing their own party for something, and even then that praise will only last so long; you could be the media's favorite Republican and you'll still be treated like the incarnation of evil the moment you become an obstacle for a Democrat seeking the White House.
You can't spend all day complaining about the media's double standard and then suddenly expect everything to go swimmingly when you try to play by the other side's rules. Any Republicans seeking higher office should take it as a given that the media will do its level best to tear them apart, and so they need to go the extra mile to make sure they have their shit together before they decide to run. A Democrat can give one speech and somehow be taken seriously as a presidential candidate, but Republicans need to do more than that. Giving a good speech or being good in a debate are good skills to have, but they shouldn't be the only skills you have. Republican candidates need to be good at communicating their ideas in simple and relatable terms, but they also need to be able to show that their ideas work when put into action, which is why governors tend to make better GOP candidates than senators do. ( People who have their hearts set on nominating a senator will often point to Mitt Romney as a notable exception, but Romney was a governor from a very blue state so he was only going to get so much mileage out of his record there... and Santorum probably would've lost by double digits anyway. )
I'm not saying that it's utterly impossible for the GOP to send a senator to the White House, just that the chances are slimmer than they should be, and when the deck is already stacked against you this much, why risk it? The media is thoroughly corrupt, probably more corrupt now than it's ever been before. Our education system is constantly churning out people who don't know how to think for themselves and our culture is constantly finding new ways to fill their heads with left-wing talking points, turning them into millions of people who are basically Democrats by default. When that's what you're fighting against, there's very little margin of error. If you really want your favorite senator to be president someday, then maybe you should be telling him to run for governor first before they run for president, or at least be willing to settle for him being on the bottom of the ticket.
( And by the way, speaking of our culture, when Republicans are already perceived as being out of touch, one of the worst ways a Republican can play the "their rules" game is to make yourself look like a culturally ignorant buffoon while throwing around blatantly false allegations of racism. )