Here’s a rule of thumb: If you are the Republican nominee and The Wall Street Journal editorial page, The Weekly Standard and The National Review are all urging you to do the same thing, run the other way. Romney doesn’t need the base; if they are not enthusiastically for him, they are enthusiastically against Obama, which ought to be enough.

Romney needs independents in Virginia, suburban women in Colorado, seniors in Florida. It’s not a question of whether Ryan will help him woo these voters; it’s a matter of whether Ryan — especially once the Obama campaign and associated super PACs get through with him — will make that even harder.

On the plus side, Ryan is smart, engaging, charismatic, young. He’s got good chemistry with Romney. He’s serious and committed without being off-putting or intractably partisan. Democrats who’ve worked with Ryan like and respect him.

But selecting him as veep doesn’t make sense. It undercuts several aspects of the Romney narrative.

Romney is the outside Washington candidate — now running with a sitting member of a body with a 12 percent approval rating. He’s the private sector fix-it guy-now with a career politician.

Most important, the choice of Ryan pushes against what has been the central theory of Romney’s campaign: make it less of a choice between himself and Obama and more of a referendum on the incumbent president and the languishing economy.

Instead, substitute endless debate and wall-to-wall advertising-on every last detail of every plan Ryan has ever put out: to add private accounts to Social Security, to change Medicare into a voucher program, to slash domestic spending to unimaginably bare-bones levels.

Why would Romney take on a fight that President Obama has been itching to have? Here was Obama in April, running against what then seemed his pipe dream ticket of Romney-Ryan: “The Republicans running Congress right now have doubled down, and proposed a budget so far to the right it makes the Contract with America look like the New Deal. In fact, that renowned liberal, Newt Gingrich, first called the original version of the budget ‘radical’ and said it would contribute to ‘right-wing social engineering.’ This is now the party’s governing platform.

“This is what they’re running on. One of my potential opponents, Gov. Romney, has said that he hoped a similar version of this plan from last year would be introduced as a bill on day one of his presidency. He said that he’s ‘very supportive’ of this new budget, and he even called it ‘marvelous’ — which is a word you don’t often hear when it comes to describing a budget.”

This is the fall conversation that Romney wants to enable?

I don’t get it. The argument for going bold, shifting gears, throwing long balls — insert cliché here — would be if the Romney campaign has concluded that it has lost the campaign-as-referendum-on-Obama argument and is panicking. But a spate of problematic national and swing stage polls notwithstanding, that seems way, way premature to me. It seems way, way premature to many Democratic strategists I’ve spoken to since the announcement.

The Ryan choice means I get to wallow in Congressional Budget Office analyses and Tax Policy Center distributional tables. It should make for a more interesting and more substantive campaign — one that may better prepare the country for the difficult fiscal choices facing the next president. I just don’t see how it helps Mitt Romney secure that job.