I’ve been bullish on Tim Pawlenty’s chances of getting the presidential nomination for some time now. But I’m starting to have second thoughts, based on the third-rate straddle of an economic “plan” he’s announced in a media blitz today.

Ezra Klein is, of course, correct that as economics, Pawlenty’plan is mostly pure fantasy. But that’s a feature, not a bug, of economic plans from GOP presidential candidates. When you’re not allowed to use real economics and are pretty much limited to “tax cuts make everything shiny” plus vows to balance the budget (while cutting taxes and revenues rather than raising them), well, of course your economic plan is going to be fantasy. It’s inescapable.

The trick for GOP candidates proposing economic plans is to promise the right things while avoiding mention of anything that is either a deal-breaker in the primaries and caucuses or highly damaging in the general election. He starts off strongly: cut taxes, and — presto magico! — you’ll get 5% annual GDP growth as far as the eye can see. And he offers everyone’s favorite nostrum for the fantasy budget cutter, a Balanced Budget Amendment. Pawlenty even has a nice innovation, substituting enhanced presidential impoundment authority for the point in the argument where one might expect a call for a line-item veto. As policy, all of this is nonsense, but it’s acceptable conservative rhetoric. Even so, it’s also easily trumped: If Newt Gingrich promised even steeper tax cuts and claimed that it would guarantee 7% annual GDP growth, where would that leave Pawlenty?

And yet — even though much of his plan is pure fantasy, it also commits the fatal error of including unnecessary specifics that could actually complicate his chances with key voters.

For instance, Pawlenty included a specific that could imperil him among GOP primary voters: “Slowing the rate of growth in defense spending.” This is anathema for conservatives: Everyone knows there’s no connection whatsoever between defense spending and deficits! Everyone knows that you can cuts taxes and increase defense spending forever without affecting the deficit at all! There’s just no reason to annoy conservatives with any responsible talk about slowing defense spending.

He also risks alienating general election voters when he proposes “raising the Social Security retirement age for the next generation.” Awful. On entitlements, the correct way to appeal to conservatives while remaining viable with the general election electorate is less specific. Both deficit idealists and Tea Party budget-cutters fully approve of “taking on entitlements” or its weaker cousin, “getting serious about entitlements.” Actually admitting to support for Social Security cuts may please conservatives now but it’s a general-election no-no.

Bottom line: There are two key takeaways from Pawlenty’s proposals. One is that they’re mostly fantasy — which is essential for GOP presidential primary contenders. The second is that where Pawlenty does get specific, he needlessly risks alienating primary and general election voters. That he hasn’t yet found a way to navigate these waters is bad news for Pawlenty indeed.