Why?

Because the premise of his entire piece is that Rush Limbaugh is, indeed, the face of the Republican Party. Look at the intro box:

The party of Buckley and Reagan is now bereft and dominated by the politics of Limbaugh. A conservative's lament.

Conceding that point isn't the strongest way to make a defense of the Republican Party. Frum goes on to convincingly argue why Limbaugh should not dominate the Republican Party, but nobody in their right mind thinks that he should. The real question is why anyone that doesn't agree with Limbaugh would embrace the GOP? Frum has no answer for that. He does offer some suggestions on how the GOP can stop the bleeding: push free-market health care instead of tax cuts, modulate positions on abortion and gays, and get an environmental message. I've made the exact same points because they are obvious points. But it's also obvious that the Republican Party is not on the cusp of doing any of those things. And I can't see how that is Rush Limbaugh's fault.

The Republican Party does have leaders. It has John McCain, for example. And it has the the minority leaders in Congress, Sen. Mitch McConnell and Rep. John Boehner. It has GOP chairman Michael Steele. It even has a few people that are well-versed in policy like Sens. Richard Lugar and Judd Gregg and Reps. Eric Cantor and Paul Ryan. The fact that none of these politicians is making an argument that is substantively distinct from Rush Limbaugh is their fault, not his.

Frum quotes Limbaugh disapprovingly:

"Conservatism is what it is, and it is forever. It's not something you can bend and shape and flake and form … I cringed—it might have been 2007, late 2007 or sometime during 2008, but a couple of prominent, conservative, Beltway, establishment media types began to write on the concept that the era of Reagan is over. And that we needed to adapt our appeal, because, after all, what's important in politics is winning elections. And so we have to understand that the American people, they want big government. We just have to find a way to tell them we're no longer opposed to that. We will come up with our own version of it that is wiser and smarter, but we've got to go get the Wal-Mart voter, and we've got to get the Hispanic voter, and we've got to get the recalcitrant independent women. And I'm listening to this and I am just apoplectic: the era of Reagan is over? … We have got to stamp this out …"

But Frum doesn't admit that the central problem for conservatives is that the country has moved on on the social issues and it does want big government. It wants to talk about regulating the financial markets, not about the wonders of the unfettered capitalism. It isn't enough to 'modulate' your position on abortion and gay rights and immigration. You have to have an answer to the economic crisis and some kind of plan to deal with global warming and energy policy. Frum at least understands that people are more concerned about escalating medical costs than tax cuts, but what about education costs?

We're entering a period of big government because small government failed us and because we're facing big problems that only the federal government is suited to address. The longer the Republican Party clings to the era of Reagan, the longer they are going to spiral downward. And that's not on Rush Limbaugh.